VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics Physics

4–7 September 2006, Lviv, Ukraine

BOOK OF ABSTRACTS

Lviv – 2006 Organizers

Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine Lviv, Ukraine

Lviv Polytechnic National University Lviv, Ukraine

Supported by

Ministry of Education and Science of Ukraine

National Academy of Sciences of Ukraine

NBU licence No. 43 from 27.01.2006 Chairmen of the Meeting Scientiﬁc Programme Committee

Zbigniew Czapla Chairmen: Institute of Experimental Physics, R.R. Levitskii (Lviv, Ukraine) Wroclaw, Poland K. Roleder (Katowice, Poland)

Ihor Stasyuk Members: Institute for Condensed Matter Physics, J. Grigas (Vilnius, Lithuania) Lviv, Ukraine B. Hilczer (Pozna´n, Poland) M.A. Korynevskii (Lviv, Ukraine) D. Michel (Leipzig, Germany) A. Pietraszko (Wroclaw, Poland) M.O. Romanyuk (Lviv, Ukraine) Meeting Secretary A.G. Slivka (Uzhgorod, Ukraine) J. Stankowski (Pozna´n, Poland) Oleh Velychko B.A. Strukov (Moscow, Russia) Institute for Condensed Matter Physics, M.P. Trubitsyn (Dnipropetrovsk, Ukraine) Lviv, Ukraine O.G. Vlokh (Lviv, Ukraine)

Organizing Committee Local Organizing Committee (ICMP, Lviv, Ukraine)

J. Dec (Katowice, Poland) M. Patsahan M.D. Glinchuk (Kyiv, Ukraine) R. Stetsiv O.L. Ivankiv (Lviv, Ukraine) Ya. Shchur I.M. Mryglod (Lviv, Ukraine) O. Vorobyov R. Poprawski (Wroclaw, Poland) T. Patsahan Yu.M. Vysochanskii (Uzhgorod, Ukraine) M. Druchok The VIII Ukrainian-Polish Meeting on Ferroelectrics Physics, organized by Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, is a regular one of the meetings devoted to physics of ferroelectrics carried out before in Ustroń-Zdrój (2004), Uzhgorod-Synjak (2002), Cracow (2000), Dnipropetrovsk (1998), Kudowa Zdrój (1996), Uzhgorod (1994), Wroc law (1992) and Lviv (1990). The Meeting will be held in Lviv by the Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine in the conference facilities of the Main Building of Lviv Polytechnic National University. The Meeting will consist of invited lectures, contributed talks and poster presenta- tions. Official language of the Meeting is English.

Main topics • Theory of ferroelectricity • Phase transitions and critical phenomena • Incommensurate phase transition • Low-dimensional systems • Ferroelectrics with hydrogen bonds • Domains and defects • Optical properties, nonlinear and photoinduced phenomena • Ferroelectrics-semiconductors, ferroelastics, superionics • Relaxors, disordered crystals, composites, ceramics • Ferroelectric applications

Contacts Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine 1 Svientsitskii Str., 79011 Lviv, Ukraine E-mail: [email protected] Tel.: +380 322 761161 Fax: +380 322 761158 URL: http://www.icmp.lviv.ua/UKR-POL8 VIII Ukrainian-Polish and III East-European Meeting

on Ferroelectrics Physics

Programme

4–7 September 2006, Lviv, Ukraine

VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Monday, September 4, 2006 Morning Sessions 10:00 – 13:50

10:00 – 10:15 Meeting opening

Session I Chaired by I.V. Stasyuk

10:15 – 11:00 J. Grigasa, E. Talikb and V. Lazauskasc X-ray photoelectron spectroscopy of ferroelectrics electronic structure aFaculty of Physics, Vilnius University, Vilnius, Lithuania bInstitute of Physics, Silesian University, Katowice, Poland cInstitute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania

11:00 – 11:45 Yu.M. Vysochanskii, L. Beley and M. Khoma Ferroelectricity in layered phosphorus chalcogenide crystals Institute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine

11:45 – 12:15 Coﬀee Break

7 4–7 September 2004, Lviv, Ukraine

Monday, September 4, 2006 Morning Sessions 10:00 – 13:50

Session II Chaired by M.V. Tkach

12:15 – 13:00 Z. Czapla, Yu. Eliyashevskyy, S. Dacko and B. Kosturek Phase transitions and ferroelectricity in [(CH3)2NH2]3CuCl5 single crystal Wroclaw University, Institute of Experimental Physics, Wroclaw, Poland

13:00 – 13:30 M.D. Glinchuka, A.N. Morozovskab and E.A. Eliseeva Size eﬀect of the properties and phase diagrams of ferroelectric cylindrical nanoparticles aInstitute for Problems of Materials Science, NAS of Ukraine, Kiev, Ukraine bV. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Kiev, Ukraine

13:30 – 13:50 D. Kaynts, A. Horvat, A.A. Grabar and M. Gurzan Domain walls in Sn2P2S6-type ferroelectrics Institute for Solid State Physics and Chemistry of Uzhgorod National University, Uzhgorod, Ukraine

13:50 – 15:00 Lunch

8 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Monday, September 4, 2006 Afternoon Sessions 15:00 – 18:10

Session III Chaired by Z. Czapla

15:00 – 15:30 J. Deca,b, W. Kleemannb, V.V. Swartsmanb and T.Lukasiewicz c Ferroelectric and relaxor behaviour in strontium-barium niobate aInstitute of Physics, University of Silesia, Katowice, Poland bAngewandte Physik, Universit¨at Duisburg-Essen, Duisburg, Germany cInstitute of Electronic Materials Technology, Warsaw, Poland

15:30 – 16:00 I.I. Grygorchaka, S. Voitovycha, I.V. Stasyukb, O.V. Velychkob and O. Menchyshynb Electret eﬀect in intercalated crystals of the AIIIBVI group aLviv Polytechnic National University, Lviv, Ukraine bInstitute for Condensed Matter Physics, Lviv, Ukraine

16:00 – 16:20 S. Miga, J. Dec and K. Cwikiel´ Temperature dependence of nonlinear dielectric susceptibilities of triglycine sulphate near ferroelectric phase transition University of Silesia, Institute of Physics, Katowice, Poland

16:20 – 16:50 Coﬀee Break

9 4–7 September 2004, Lviv, Ukraine

Monday, September 4, 2006 Afternoon Sessions 15:00 – 18:10

Session IV Chaired by I.P. Studenyak

16:50 – 17:30 Yu.F. Markova, K. Knorrb and E.M. Roginskiia Phase transitions, order parameters and their ﬂuctuations in the model ferroelastic crystals aA.F. Ioﬀe Physical-Technical Institute, St. Petersburg, Russia bUniversitat des Saarlandes, Saarbruecken, Germany

17:30 – 17:50 V.S. Shusta, I.P. Prits, P.P. Guranich and E.I. Gerzanich Dielectric properties of CuInP2S2 crystals under high pressure Uzhhorod National University, Optics Department, Uzhhorod, Ukraine

17:50 – 18:10 A. Hek, S. Dacko and Z. Czapla Dielectric properties in BA crystal Wroclaw University, Institute of Experimental Physics, Wroclaw, Poland

18:15 – 21:00 Get-together party

10 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Tuesday, September 5, 2006 Morning Sessions 9:30 – 13:20

Session V Chaired by B. Strukov

9:30 – 10:15 D. Michel NMR and EPR study of phase transitions in conﬁned geometry University Leipzig, Institute of Experimental Physics II, Leipzig, Germany

10:15 – 11:00 M. Tkach, Ju. Seti and M. Rud’ko Exciton in closed and opened quantum dot Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, Chernivtsi, Ukraine

11:00 – 11:20 Ya. Shchur Phonon dynamics and speciﬁc heat of CsH2PO4 and CsD2PO4 crystals Institute for Condensed Matter Physics, Lviv, Ukraine

11:20 – 11:50 Coﬀee Break

11 4–7 September 2004, Lviv, Ukraine

Tuesday, September 5, 2006 Morning Sessions 9:30 – 13:20

Session VI Chaired by J. Dec

11:50 – 12:20 A. Pietraszko and K.Lukaszewicz Diﬀused scattering and short range order in the paraelectric phase of sodium nitrite Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw, Poland

12:20 – 12:50 R. Hrabanski´ a, M. Janiec-Matejaa and Z. Czaplab EPR study of local ordering in DMAAS and DMAGS crystals aInstitute of Physics, Cz¸estochowa University of Technology, Cz¸estochowa, Poland bWroclaw University, Institute of Experimental Physics, Wroclaw, Poland

12:50 – 13:20 M.P. Trubitsyna, S. Waplakb and Yu.D. Krokhmal’a EPR of the Gd3+ probe near ferroelectric phase transition in Pb5Ge3O11 aDepartment of the solid state physics, Dnipropetrovsk National University, Dnipropetrovsk, Ukraine bInstitute of Molecular Physics, Pozna´n, Poland

13:20 – 15:00 Lunch

12 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Tuesday, September 5, 2006 Afternoon Sessions 15:00 – 19:30

Session VII Chaired by D. Michel

15:00 – 15:40 B. Strukov, I. Shnaidshtein and S. Grabovsky Phase transitions in KDP crystals with the complex organic and inorganic impurities Lomonosov Moscow State University, Moscow, Russia

15:40 – 16:10 R.R. Levitskiia, S.I. Sorokova, Z. Trybulab and A.S. Vdovycha Thermodynamics and relaxation dynamics of the Rb1−x(NH4)xH2PO4 type proton glasses aInstitute for Condensed Matter Physics, Lviv, Ukraine bInstitute of Molecular Physics, Polish Academy of Sciences, Pozna´n, Poland

16:10 – 16:40 Coﬀee Break

13 4–7 September 2004, Lviv, Ukraine

Tuesday, September 5, 2006 Afternoon Sessions 15:00 – 19:30

Session VIII Chaired by Yu.M. Vysochanskii

16:40 – 17:10 M. Kozlovskii Critical behaviour of the susceptibility and heat capacity of the 3D Ising systems at the presence of an external ﬁeld Institute for Condensed Matter Physics, Lviv, Ukraine

17:10 – 17:40 N.D. Baysaa, I.M. Rizakb, V.S. Bilanychc, Z. Trybulad, V.M. Holoveye and V.M. Rizakc Studies of transfer phenomena in Li2B4O7 aNational Aviation University, Kyiv, Ukraine bDnipropetrovsk National University, Dnipropetrovsk, Ukraine cUzhgorod National University, Uzhhorod, Ukraine dInstitute of molecular physics of the Polish academy of sciences, Poznan, Poland eInstitute of Electron Physics NAS of Ukraine, Uzhhorod, Ukraine

Session IX Chaired by I.V. Stasyuk, Z. Czapla, D. Michel and Yu.M. Vysochanskii

17:40 – 19:30 Poster Session

14 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Wednesday, September 6, 2006 Morning Sessions 9:30 – 13:15

Session X Chaired by V. Biedrzycki

9:30 – 10:15 J. Stankowski Rotation degree of freedom for the motion of glycine molecule Institute of Molecular Physics, Polish Academy of Sciences, Pozna´n, Poland

10:15 – 10:45 M. Piasecki, I.V. Kityk and K. Ozga Correlation between DSC and non-linear optical monitoring of the phase transitions Institute of Physics, J. Dlugosz University Czestochowa, Czestochowa, Poland

10:45 – 11:15 R. Vlokh and O. Mys Combined crystalooptical eﬀects in ferroelectrics and ferroelastics Institute of Physical Optics, Lviv, Ukraine

11:15 – 11:45 Coﬀee Break

15 4–7 September 2004, Lviv, Ukraine

Wednesday, September 6, 2006 Morning Sessions 9:30 – 13:15

Session XI Chaired by M. Kozlovskii

11:45 – 12:15 N.A. Korynevskiia,b and V.B. Solovyana Investigation of ferroelectric-antiferroelectric mixed compounds aInstitute for Condensed Matter Physics, Lviv, Ukraine bInstitute of Physics, University of Szczecin, Szczecin, Poland

12:15 – 12:45 Z. Bak Landau-Ginzburg theory of phase transitions on fractal systems Institute of Physics, JD University of Czestochowa, Czestochowa, Poland

12:45 – 13:15 A.N. Morozovskaa, E.A. Eliseevb, D. Remiensc and C. Soyerc Pyroelectric and ferroelectric hysteresis in the ferroelectric-semiconductor ﬁlms with charged defects aV. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kiev, Ukraine bInstitute for Problems of Materials Science, National Academy of Science of Ukraine, Kiev, Ukraine cIEMN, UMR 8520 OAE-dept/ MIMM, Universite de Valenciennes et du Hainaut-Cambresis, Valenciennes, France

13:15 – 14:30 Lunch

14:30 – 18:00 Sightseeing of Lviv

19:00 – 22:00 Conference dinner

16 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Thursday, September 7, 2006 Morning Sessions 9:30 – 13:20

Session XII Chaired by R. Levitskii

9:30 – 10:10 B. Koniecznaa, M. Cichab and K. Biedrzycki Pyroelectric electron and X-ray generator – a review aUniversity of Wroclaw, Institute of Experimental Physics, Wroclaw, Poland bUniversity of Zielona G´ora, Institute of Physics, Zielona G´ora, Poland cUniversity of Opole, Institute of Physics, Opole, Poland

10:10 – 10:50 M. Kharchenko Magnetoelectric multiferroics: present-day reality and promises Institute for Low Temperature Physics and Engineering, NASU, Kharkiv, Ukraine

10:50 – 11:20 R.R. Levitskiia, I.R. Zachekb, A.P. Moinaa and A.S. Vdovycha Role of piezoelectricity in relaxational and other dynamical properties of ferroelectrics aInstitute for Condensed Matter Physics, Lviv, Ukraine bLviv Polytechnical National University, Lviv, Ukraine

11:20 – 11:50 Coﬀee Break

17 4–7 September 2004, Lviv, Ukraine

Thursday, September 7, 2006 Morning Sessions 9:30 – 13:20

Session XIII Chaired by M. Trubitsyn

11:50 – 12:20 O. Krupych, Ya. Dyachok, I. Smaga and R. Vlokh Anisotropy of laser-induced bulk damage of single crystals Institute of Physical Optics, Lviv, Ukraine

12:20 – 12:40 I. Martynyuk-Lototskaa, O. Mysa, O. Krupycha, V. Adamiva, Ya. Buraka, R. Vlokha, O. Vlokha and W. Schranzb Borate crystals – new high efficient acoustooptic materials aInstitute of Physical Optics, Lviv, Ukraine bInstitut für Experimentalphysik, Universität Wien, Wien, Austria

12:40 – 13:00 R.Z. Rogowski and K. Matyjasek Polarization relaxation in non-uniform ferroelectric crystals Institute of Physics, Szczecin University of Technology, Szczecin, Poland

13:00 – 13:20 I.V. Stasyuk and O. Vorobyov Metal-insulator like transition in energy spectrum of one-dimensional proton (ionic) conductor Institute for Condensed Matter Physics, Lviv, Ukraine

13:20 – 15:00 Lunch

18 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Thursday, September 7, 2006 Afternoon Session 15:00 – 15:50

Session XIV Chaired by V.M. Rizak

15:00 – 15:30 A.G. Slivka, I.P. Studenyak, O.O. Gomonnai, I.Yu. Kuritsa and P.P. Guranich IV V VI Speciﬁc features of optical absorption processes in A2 B2 C6 ferroelectrics Uzhhorod National University, Optics Department, Uzhhorod, Ukraine

15:30 – 15:50 V.B. Kapustyanyk and V.P. Rudyk Radiochromic phenomena in the ferroics with transition metal ions Ivan Franko National University of Lviv, Scientiﬁc-technical and Educational Center of Low Temperature Studies, Lviv, Ukraine

16:00 Closing of the Meeting

VIII Ukrainian-Polish and III East-European Meeting

on Ferroelectrics Physics

Lectures

4–7 September 2006, Lviv, Ukraine

Monday, September 4 L1

X-ray photoelectron spectroscopy of ferroelectrics electronic structure J. Grigasa, E. Talikb and V. Lazauskasc aFaculty of Physics, Vilnius University, Sauletekio Ave. 9/3, LT–10222 Vilnius, Lithuania, E–mail: jonas.grigas@ﬀ.vu.lt bInstitute of Physics, Silesian University, Universytetska 4, 40–007 Katowice, Poland cInstitute of Theoretical Physics and Astronomy, Vilnius University, Gostauto 12, LT–01108 Vilnius, Lithuania

were analyzed in the range 0–1400 eV. Experimen- Tl 4f 195 K tally obtained energies were compared with the results of theoretical ab initio calculations by the Hartree-Fock method for a molecular model of the crystal. Two kinds of phenomena are discussed: 1. The resolved splitting of the CL in the in- 203 K commensurate (IC) phase of TlInS2 (Fig. 1). 2. Electronic structure of the VB and CL splitting in the quasi-one-dimensional SbSI-type crystals [1,2]. The VB of SbSI, BiSI and SbSeI are similar, and are composed from the s- and p- 206 K bands. The s-band is formed from Sb 5s, S(Se) 3s and I 5s states. The p-band is formed from S(Se) 5p, Sb 5p and I 5p states. The VB form depends

Intensity (a.u.) Intensity on the population of energy levels of surface and bulk atoms. Conduction band (CB) edge is formed almost 100% by the Sb 5p surface states. The ob- 210 K tained theoretical density of states and the VB form is close to the experimental XPS (Fig. 2). Large CL splitting was obtained in SbSI due to diﬀerent valence state of bulk and (001) surface 300 K atoms.

110 115 120 125 130

Binding energy (eV) Figure 1: Splitting of the Tl 4f spin-orbit doublet in the IC phase (195–210 K) of TlInS2 crystal. In this talk we discuss the X-ray photoelectron spectroscopy (XPS) of the valence band (VB) and core-levels (CL) form and electronic structure Figure 2: Electronic structure of SbSI VB. D(ε) is in ferroelectrics. The excitation source of the PHI the density of states. VB is approximated by the 5700/660 Physical Electronics Spectrometer was Gaussian broadening method for SbSI molecular monochromatic Al Kα radiation (1486.6 eV). XPS clusters from 2 (bottom dotted) to 16 (top solid).

1. J. Grigas, E. Talik, and V. Lazauskas, Lithuanian J. Phys. 44, 427 (2004). 2. V. Lazauskas, V. Nelkinas, J. Grigas, E. Talik, and V. Gavryushin, Lithuanian J. Phys. 46, Nr. 2 (2006).

23 L2 Monday, September 4

Ferroelectricity in layered phosphorus chalcogenide crystals

Yu.M. Vysochanskii, L. Beley and M. Khoma Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyna Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected]

In layered crystals CuInP2S6 a first order phase transition occurs at Tc ≈ 310 K. Also second order transition near 330 K was observed. In paraelectric phase, with symmetry C2/c, Curie-Weiss constant C ≈ 5 · 103 K that is characteristic for order/disorder type of transitions. At T < Tc, in the ferrielectric phase with symmetry −2 Cc, the spontaneous polarization Ps ≈ 2.5 µC cm . For crystals CuInP2Se6 also two consecutive phase transitions were observed: second order at Ti ≈ 249 K and first or- 3 der at Tc ≈ 235 K. In the paraelectric phase (P −31c) C ≈ 1.7 · 10 K. At T < Tc, in −2 the ferrielectric phase with symmetry (P 31c) Ps ≈ 1.3 µC cm . In both sulfide and selenide compounds the spontaneous polarization vector is oriented normally to the structure layers and is determined by two anticollinear contributions from Cu+ ions ordering and In3+ ions shifting. A morphotropic phase boundary between C2/c and P −31c paraelectric phases or Cc and P 31c ferrielectric phases in the concentration-temperature diagram of the CuInP2(SexS1−x)6 solid solutions is located in the region between x = 0.3 and 0.4. For mixed crystals with x< 0.75 clearly the dipole glassy behavior is observed. Investigated phase transitions are analyzed in a mean-field approach.

24 Monday, September 4 L3

Phase transitions and ferroelectricity in [(CH3)2NH2]3CuCl5 single crystal Z. Czapla, Yu. Eliyashevskyy, S. Dacko and B. Kosturek Wroclaw University, Institute of Experimental Physics, Max Born Sq. 9, 50–204 Wroclaw, Poland, E–mail: [email protected]

The detailed studies of dielectric properties of [(CH3)2NH2]3CuCl5 single crystal were performed. Distinct anomalies of permittivity along three crystallographic direction were observed at about 277.5 K and 252.7 K on cooling. The observed permittivity behaviour evidenced the first order character of both phase transitions. The hysteresis loops characteristic of a ferroelectric phase were observed in the range of temperature 277.5–252.7 K. An appearance and disappearance of spontaneous polarization confirms the first order phase transitions in this crystal. The permittivity measured along the ferroelectric a-axis under influence of external electric field in paraelectric phase showed clearly a nonlinear increase with increase of electric field intensity applied to the crystalline sample. Dilatometric measurement of thermal expansion and birefringence measurement showed clearly two successive phase transitions at T1 = 278.3 K and T2 = 253.4 K on cooling run with thermal hysteresis The obtained changes of ∆V/V are equal to (2.37 ± 0.15) · 10−3 at 278.3 K and (2.61 ± 0.15) · 10−3 at 253.4 K, respectively. Anomalies of linear birefringence confirm the first-order character of both phase transitions. The temperature of phase transitions and temperature hysteresis depends on cooling/heating rate.

25 L4 Monday, September 4

Size eﬀect of the properties and phase diagrams of ferroelectric cylindrical nanoparticles

M.D. Glinchuka, A.N. Morozovskab and E.A. Eliseeva aInstitute for Problems of Materials Science, NAS of Ukraine, Krjijanovskogo 3, 03142 Kiev, Ukraine, E–mail: [email protected], [email protected] bV. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauki 41, 03028 Kiev, Ukraine, E–mail: [email protected]

The ferroelectric phase was studied experimentally in ferroelectric nanotubes, nanowires and nanorods. It is appeared that cylindrical geometry does not destroy ferroelectric phase as predicted and observed for spherical particles, but sometimes the noticeable enhancement of ferroelectric properties appears in cylindrical nanoparticles. In particular, nanotubes and nanorods posses such polar properties as remnant polarization and high piezoelectric coefficient. In this paper we study theoretically the size effects of the ferroelectric nanotubes, nanorods and nanowires phase diagrams allowing for the effective surface tension and depolarization field influence. We suppose that the surface charges screen the surrounding medium from the nanoparticle electric field so that it is possible to neglect the interactions of the particles. The approximate analytical expression for the paraelectric-ferroelectric transition temperature dependence on nanoparticle radii, length, polarization gradient coefficient, extrapolation length, effective surface tension and electrostriction coefficient was derived. It was shown that the transition temperature could be higher than the one of the bulk material for perovskites. We obtained, that the surface tension coupled with polarization via electrostriction effect is key to the ferroelectricity enhancement in confined nanotubes, nanowires and nanorods. Therefore we predict conservation and enhancement of ferroelectric properties in long cylindrical nanoparticles. Obtained results could be very useful for tailoring of ferroelectric nanocomposites with perfect polar properties.

26 Monday, September 4 L5

Domain walls in Sn2P2S6-type ferroelectrics D. Kaynts, A. Horvat, A.A. Grabar and M. Gurzan Institute for Solid State Physics and Chemistry of Uzhgorod National University, 46 Pidhirna Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected]

The static domain structure of the Sn2P2(SexS1−x)6 uniaxial proper ferroelectrics has been studied by using the AFM, chemical etching and optical techniques. The Sn2P2S6 crystals undergo a second order phase transition from 2/m to m point group at 66◦C, and the transition temperature goes down at S–Se substitution, reaching ◦ ≈ 26 C in the Sn2P2(Se0.2S0.8)6 solid solution. This substitution is accompanied by approaching to the Lifshitz point (at x = 0.28) on the “temperature-compound” phase diagram of these mixed crystals, that is defined by the variation of the interaction of the order parameter fluctuation (polarization) with deformations. It was found that the equilibrium domain walls are formed by two kinds of the walls: first ones, inclined relative to spontaneous polarization vector on an angle about 10–12 degrees (charged walls), and second one, which are parallel to the symmetry plane. The presence of the charged walls is well confirmed by studies of the etching and AFM figures obtained on various cuts of the samples. The possibility of the existence of the charged domain walls in an equilibrium state is explained by its screening by charge carriers. In this case their orientations are defined mainly by the minimum of the elastic contribution to the wall energy. This feature makes possible an observation of the light reflection on the layers, formed by charge carriers screening charged domain walls between opposing 180◦ domains, that permits to determine easily its orientation in the bulk of the crystals. The variation of the wall orientation with S–Se substitution was determined by the both light reflection and etching methods. Basing on the available data on the elastic tensor anisotropy and other properties, the possible orientations of the charged wall were analyzed numerically.

27 L6 Monday, September 4

Ferroelectric and relaxor behaviour in strontium-barium niobate

J. Deca,b, W. Kleemannb, V.V. Swartsmanb and T.Lukasiewicz c aInstitute of Physics, University of Silesia, Katowice, Poland, E–mail: [email protected] bAngewandte Physik, Universit¨at Duisburg-Essen, Duisburg, Germany cInstitute of Electronic Materials Technology, Warsaw, Poland

Results of systematic investigations of the dielectric response measured along the polar c-axis of the four single crystalline strontium-barium niobate, SrxBa1−xNb2O6, with nominal x = 0.45, 0.50, 0.61, and 0.75 designated hereafter as SBN40, SBN50, SBN61, and SBN75, respectively are presented. In accordance to expectation, temperature dependences of the linear dielectric susceptibility measured within 10−2 ≤ f ≤ 105 Hz reveal a gradual crossover from the conventional ferroelectric (SBN40) to extreme relaxor (SBN75) behaviour. Analysis of the data within the framework of the activated dynamic scaling law shows that the Curie point of ferroelectric SBN40 is a linear extrapolation of the freezing temperatures determined for the other SBN crystals. Correspondingly, a change from the “normal” compact domains to the smaller ones with jagged (fractal-like) boundaries was revealed by piezoresponse force microscopy (PFM). The dielectric spectra of SBN61 and SBN75 reveal two distinct slow dynamics modes, viz. “wall segment relaxation” and “creep”. They refer to the borders of mesoscopic polar nanoregions (PNRs) embedded in the neutral paraelectric environment. Due to their very broad size distribution the largest PNRs become visible by PFM. From the nonlinear dielectric response the nonlinearity coeﬃcient B appearing in the equation of state, E = AP + BP 3, is determined. It is found to vanish when approaching the phase transition point even in the extreme relaxor crystal. This kind of behaviour shows that the uniaxial SBN relaxor cannot be considered as a dipole glass system. Instead, it can be mapped onto the order-disorder 3D random-ﬁeld Ising model since SBN lacks any optic soft mode. Financial support by KBN (under grant 4 T08A 007 25) and DFG (SPP “Struk- turgradienten in Kristallen”) is gratefuly acknowledged.

28 Monday, September 4 L7

Electret eﬀect in intercalated crystals of the AIIIBVI group

I.I. Grygorchaka, S. Voitovycha, I.V. Stasyukb, O.V. Velychkob and O. Menchyshynb aLviv Polytechnic National University, 12 Bandera Str., 79013 Lviv, Ukraine, bInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine

The polarization state of the electret type, revealed previously in the AIIIBVI group crystals (of the GaSe and InSe type) intercalated by alkali metals, is considered. The effect manifests himself as appearance of the non-zero electrical potential difference ∆ϕ in the direction of c-axis (perpendicularly to the atomic layers); the magnitude and the sign of the latter depends on the sort of introduced atoms and their concentration x. A nonmonotonic character of the ∆ϕ(x) dependence and the essential decrease of its magnitude at higher intercalant concentrations (x > 0.005) are revealed in nickel- intercalated compounds NixInSe and NixGaSe. The maximum value of ∆ϕ for NixGaSe in the temperature range from −40◦C to +60◦C corresponds to the lowest temperature and reaches 3.89 V. More than ten-fold increase of the dielectric permittivity εc in the frequency region 10−3−106 Hz and an anomalous (up to several orders) x-dependent enhancement of εc at frequencies below 100 Hz are established by impendance spectroscopy. The temperature dependence of εc on T exhibits a pronounced maximum. Its position is changed with the Ni concentration; in the case of NixInSe the maximum εc(T ) disappears completely at the increase of x from 0.004 up to 0.006. In our opinion, the observed electret effect is connected with the presence of local quasi-dipoles (intercalated ion plus nearest anion, surrounded by redistributed charge carriers) oriented in the certain prevailing direction. An assumption is made that the lowering of the system symmetry takes place due to the redistribution of “guest” atoms between centrosymmetric (octahedral) and noncentrosymmetric (tetrahedral) positions. The corresponding microscopic 4-state model, which is a generalization of the well-known Blume-Emery-Griffitts model, is proposed. The thermodynamic functions are calculated; temperature and concentrational dependences of polarization of the system and occupancies of various positions are investigated. Phase transitions, connected with the jump-like change of the intercalate concentration x, with the appearance of the spontaneous dipole moment are revealed; appropriate phase diagrams are built. The calculated temperature dependences εc(T ) exhibit (depending of x) a possibility of appearance of a sharp maxima, caused by passing close to lines of critical points.

29 L8 Monday, September 4

Temperature dependence of nonlinear dielectric susceptibilities of triglycine sulphate near ferroelectric phase transition

S. Miga, J. Dec and K. Cwikiel´ University of Silesia, Institute of Physics, ul. Uniwersytecka 4, 40–007 Katowice, Poland, E–mail: [email protected]

The linear, second-order, and third-order, dielectric susceptibilities χ1, χ2, χ3, of triglycine sulphate (TGS) single crystal have been measured using dynamic method [1]. The second-order dielectric susceptibility has non-zero value in ferroelectric phase only and vanishes at temperature of ferroelectric phase transition. The change in the sign of the third-order dielectric susceptibility, χ3, as predicted by the thermodynamic theory of the continous phase transitions [2] is conﬁrmed experimentally. Nonlinearity 1 coeﬃcient, B, which appears in the expansion of the free energy: F = Fo + 2 AP + 1 4 4 BD + . . . has been evaluated with the use of the following equation [3]:

1 χ3 3 4 for T < Tc,  8o χ1 B =   1 χ  − 3 for T > T . 3 χ4 c  o 1   Both, the change in the sign of χ3 and the temperature independence of the nonlinearity coeﬃcient, B, within the temperature range of T ≤ TC +2K above the phase transition temperature point, conﬁrm that the TGS belongs to the Landau universality class.

1. J. Dec, W. Kleemann, S. Miga, C. Filipiˇc, A. Levstik, R. Pirc, T. Granzow and R. Pankrath, Phys. Rev. B 68, 092105 (2003). 2. S. Ikeda, H. Kominami, K. Koyama and Y. Wada, J. Appl. Phys. 62, 3339 (1987). 3. S. Miga, J. Dec and A. Molak, J. Appl. Phys. 99, (2006).

30 Monday, September 4 L9

Phase transitions, order parameters and their ﬂuctuations in the model ferroelastic crystals

Yu.F. Markova, K. Knorrb and E.M. Roginskiia aA.F. Ioﬀe Physical-Technical Institute, 194021 St. Petersburg, Russia, E–mail: [email protected]ﬀe.ru bUniversitat des Saarlandes, Saarbruecken–6600, Germany

The univalent-mercury halide crystals Hg2Hal2 (Hal = Cl, Br, I) were used as model objects in these investigations. The improper ferroelastic phase transitions (PT) 17 17 D4h → D2h were observed at Tc = 186 K (Hg2Cl2) and Tc = 144 K (Hg2Br2). These PT were induced by the soft-TA mode condensation at the X-point of the Brillouin zone boundary of the tetragonal paraphase, accompanied by doubling of the unit cell and the X → Γ folding in the Brillouin zone. The fundamental and diffuse reflections in the Hg2Hal2 crystals was studied by the X-ray structure analysis. At the X-points of the paraphase Brillouin zone the diffuse X-ray scattering discovered and studied on cooling. The appearance of the scattering at the X-points, forbidden in paraphase, induced by the spatiotemporal order-parameter fluctuations corresponding to the soft TA mode at the X points of the Brillouin zone boundary and bound with nucleation of low-temperature orthorhombic nanoclusters in the high-temperature tetragonal paraphase matrix. At the cooling the clusters are growing and form the two-dimensional long-periodic superstructure interacting elasti- cally. At T = Tc through chaotic state the last one transforms into low-temperature domains. The diffuse maxima at the X-points of a Brillouin zone at phase transition (T < Tc) and “X → Γ” folding transform to fundamental reflexes. The temperature behaviour of last ones characterizes already behaviour of an order parameter. In result of these study the original information about the temperature behaviour of the order parameter and the critical exponent values were obtained. From temperature behaviour of a diffuse scattering, bound with fluctuations of an order parameter, the temperature dependences and quantities of susceptibility, correlation radius, shape and sizes of nanoclusters, the relevant critical exponents were spotted. The model of the phase transitions near tricritical point was discussed. This work was supported in part by RFBR (Grant No. 05–08–33431) and Programs of Presidium of RAS (P–03).

31 L 10 Monday, September 4

Dielectric properties of CuInP2S6 crystals under high pressure

V.S. Shusta, I.P. Prits, P.P. Guranich and E.I. Gerzanich Uzhhorod National University, Optics Department, 54 Voloshyn Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected]

While physical properties of “3-D” Sn2P2S6-type crystals at high hydrostatic pressures have been studied rather extensively, investigations of “2-D” (layered) structures based on these crystals under high pressure are at the initial stage. Studies of ferroelectric phase transitions in CuInP2S6 layered crystals at atmospheric pressure [1] have shown that ferroelectric polarization in these crystals arises due to a ﬁrst-order phase transition, normally to the layers, and results from anticolinear contributions due to copper ion ordering and indium ion displacement. Here we report on the studies of eﬀect of high hydrostatic pressure (patm

1. A. Simon, J. Ravez, V. Maisonneive, C. Payen, V.B. Cajipe, Chem. Mater. 6, 1675 (1994).

32 Monday, September 4 L 11

Dielectric properties in BA crystal

A. Hek, S. Dacko and Z. Czapla Wroclaw University, Institute of Experimental Physics, Max Born Sq. 9, 50–204 Wroclaw, Poland, E–mail: [email protected]

Dielectric measurements for single crystal of betaine arsenate (CH3)3NCH2COO · H3AsO4 (abbreviated to BA) connected with the ferroelectric phase transition at 119 K were performed. The temperature dependence of electric permittivity was measured at dc electric fields up to 700 kV/m. The results show significant suppression of the dielectric constant by the application of dc field. The electric permittivity was also measured in the paraelectric phase at constant temperature as a function of electric field intensity up to 700 kV/m. The main conclusions of this analysis is that dielectric permittivity of BA can be described by the state equation of the classical theory in the range of temperature 130–152 K. Then the relation ε0(E) was improved by additional term E6, which let us describe ε0(E) in the range of temperature 126–152 K. Finally, it was necessary to add clusters’ term in order to explain deviation from usual dependence of electric permittivity in lower temperatures. The fit parameters indicates that the polar-cluster carries polarization P = (0.7−4.9) · 10−3 C m−2 with the cluster size of L = 12−20 nm.

33 L 12 Tuesday, September 5

NMR and EPR study of phase transitions in conﬁned geometry

D. Michel University Leipzig, Institute of Experimental Physics II, Linn´estrasse 5, 04103 Leipzig, Germany, E–mail: [email protected]

The aim of the contribution is to present examples of our recent research on nano-structered materials. It will include the study of the influence of size effects on the ferroelectric properties of oxide perovskites. These investigations have obtained a great impetus in recent years because Curie temperature, electrical polarization, coercive field, switching time and other properties potentially depend on the particle size. It will be shown that the EPR and NMR methods sensitively probe changes of the structure and the local symmetry in the nanocrystalline material. The contribution will also include recent studies on the behaviour of of BaTiO3 and NaNO2 in mesoporous materials, and of glass-forming molecules in confined geometry. The properties of BaTiO3 powders will be investigated by means of NMR spectroscopy. The advantage is that these studies may be performed on natural local probes, e.g. on 137Ba nuclear spins. Central transition (mI = −1/2 ⇔ mI = +1/2) NMR spectra are measured the line shape of which is dominated by the nuclear quadrupole interaction in second order of the perturbation theory. This has been checked by measurements at various 137Ba Larmor frequencies. It will be shown that the 137Ba quadrupolar coupling constant e2qQ/h in the tetragonal phase allows similar conclusions about the properties of the fine particles as the fine structure parameter D. On this basis a structural model for a nanograin is derived in which a only weakly distorted tetragonal core is surrounded by a highly distorted shell. Moreover, we explain the application of multi-frequency EPR to BaTiO3 2+ 3+ doped by Mn ions and to PbTiO3 doped with Cr ions. Ultrafine powders are prepared from a monomeric metallo-organic precursor through combined-solid state polymerization and pyrolysis (CPP). The mean particle diameter dm was varied in the range between ca. 10 nm and 250 nm. This particular route enables not only the adjustment of the mean particle size but also the incorporation of the paramagnetic metal ions. The perovskite nanopowders were carefully characterized by various methods (TGA, DSC, FT-Raman, XRD, SEM and EDX). The mean fine structure parameter D and the widths ∆D of the distribution reveal a pronounced size dependence. Critical particle diameters for the disappearance of ferroelectricity in these fine perovskite powders are estimated. Moreover, we study the behavior of BaTiO3 embedded into mesoporous MCM 41 materials. The materials used possess an effective diameter of the hexagonal tubes of ca. 3.7 nm. In contrast to the large dielectric constants (d.c.) measured for the bulk BaTiO3 in the tetragonal phase, the d.c. values of these materials practically do not differ from those ones for empty MCM 41 rods. The behavior shows that the materials do not reveal ferroelectric properties. This conclusion is quite consistent with the critical diameters estimated for fine BaTiO3 powders. It is also the aim to present an overview about the recent work on NaNO2 in porous MCM41 and SBA materials and the glass transition of glass forming molecules in zeolites and related mesoporous materials. Acknowledgement I greatly acknowledge the important contributions to this lecture by Prof. R. Boettcher (Leipzig), Prof. E. V. Charnaya (St. Petersburg), Dr. E. Erdem (Leipzig), Dipl.-Phys. O. Erdem (Leipzig), Dr. E. Hartmann (Leipzig, Leibniz Institute for Surface Modification), Dipl.-Phys. G. Klotzsche (Leipzig), and M. Sc. P. Sedykh (Leipzig and St. Petersburg). I am greatly indebted to Prof. J. Haase for valuable comments and for his support of this work.

34 Tuesday, September 5 L 13

Exciton in closed and opened quantum dot

M. Tkach, Ju. Seti and M. Rud’ko Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, 2 Kotsubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

The theory of exciton spectra in complicated closed quantum dots is developed in details. Nevertheless, the strait theory is absent even for the simple opened quantum dot due to the principal mathematical difficulties arising at the solution of Schrodi- nger problem for the interacting electron and hole. In order to avoid the difficulties of the S-matrix calculation for the interacting quasiparticles in opened nanosystem, it is observed the three shell closed spherical quantum dot (two wells and one barrier) with the finite potential barriers. The spectra and wave functions of non interacting electron and hole in closed nanosystem are calculated exactly. Using this information the Coulomb interaction between electron and hole in complicated closed nanosystem is taken into account. There are established the electron and hole spectra in closed system as functions of the external well width in order to obtain the quasistationary exciton spectrum in opened nanosystem (resonance energies and bands semiwidth). The numeric calculations for the HgS/CdS/HgS/CdS nanosystem prove that at rather big thicknesses of this well (3–5 µm) the electron and hole spectra are so thicken near the respective resonance states that the distribution of probability of the location of both quasiparticles in the internal part of quantum dot is Lorentz like, therefore such system can be assumed as opened one. In the paper it is shown that the exciton quasistationary states are created only when electron and hole orbital quantum numbers are equal, the energy of electron-hole interaction is decreasing and limits to the finite magnitude at the increasing of the external well width and the semiwidths of exciton bands in quantum dot with rather wide external wells are decreasing and in the limit case reach the semiwidths equal to the sum of the respective semiwidths of electron and hole bands in opened spherical quantum dot.

35 L 14 Tuesday, September 5

Phonon dynamics and speciﬁc heat of CsH2PO4 and CsD2PO4 crystals Ya. Shchur Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

This contribution contains the results of lattice dynamics simulation of monoclinic CsH2PO4 and CsD2PO4 crystals in paraelectric (P 21/m, Z = 2), ferroelectric (P 21, Z = 2) and antiferroelectric (P 21/a, Z = 4) phase. The simulation was performed within the atomistic approach taking into consideration long-range Coulomb, short- range Born-Mayer type, covalent and van der Waals interactions. The oxygen-hydrogen interactions within hydrogen bonds were assumed by means of covalent-like potential. Phonon dispersion relations, partial density of states, velocities of ultrasonic waves and atomic displacement parameters were calculated in all structural phases. There are rather contradictory experimental data concerning the temperature dependence of specific heat of CsH2PO4 and CsD2PO4 presented by two groups of authors (J. Phys.: Solid State Phys., 15, 6823 (1982) and J. Phys. Soc. Jpn., 52, 3960 (1983)). The difference was observed not only in the temperature dependence of CP but even in the magnitude of CP (the difference reaches 25 % for CsH2PO4). The present simulation aims to clarify the temperature evolution of specific heat of these compounds. The reasonable agreement between the simulation and experiment for structural, spectroscopic and acoustic data obtained within the current simulation enable us to suppose that the real temperature dependence of specific heat of CsH2PO4 and CsD2PO4 crystals should be close to that simulated by us. However, the additional experimental data could answer this question finally.

36 Tuesday, September 5 L 15

Diﬀused scattering and short range order in the paraelectric phase of sodium nitrite

A. Pietraszko and K.Lukaszewicz Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw, Poland

The crystal structure of NaNO2 is studied using diffused X-ray scattering technique at ambient temperature. Ferroelectricity was revealed in NaNO2 by Sawada (1958) and ferroelectric-paraelectric phase transition temperature appears at TC ≈ 436 K. An intermediate incommensurate phase between ferro- and paraelectric phases was reported by Kucharczyk et al. (1980). In 1963 Canut and Hoseman [1] found in NaNO2 thermal diffused pattern characteristic of ionic crystals. The incommensurately modulated antiferroelectric phase of sodium nitrite, NaNO2, transforms at TN = 437.7 K to the short-range modulated paraelectric phase [2]. The apparently discontinuous phase transition is accompanied by characteristic changes in the diffraction pattern. Contrary to the well known modulated structures with sharp satellite reflections, the diffraction pattern of a short-range modulated structure contains diffuse satellite reflections. The short-range modulated crystal structure of the paraelectric phase of sodium nitrite has been analysed by the Reverse Monte Carlo (RMC) simulation of X-ray diffuse scattering. The crystal structure of sodium nitrite may be regarded as consisting of [Na+NO2]1 rows running along the polar b axis. One can expect long fragments of rows with uniform polarity The assumption that single [Na+NO2]1 rows are polar with uniform polarity proved to be a convenient approximation which is in good agreement with the observed diffraction pattern. The distribution of (+)- and (−)-[Na+NO2]1 polar rows crossing the (010) plane of short-range modulated NaNO2 revealed by RMC shows nanodomains consisting of distorted fragments of a sinusoidally modulated crystal structure. The size of the nanodomains and the degree of order in paraelectric NaNO2 decreases with temperature.

1. M. Canut, R. Hoseman, Acta Cryst. 17, 973 (1964). 2. K. Lukaszewicz, A. Pietraszko Acta Cryst. B61, 473, (2005).

37 L 16 Tuesday, September 5

EPR study of local ordering in DMAAS and DMAGS crystals

R. Hraba´nskia, M. Janiec-Matejaa and Z. Czaplab aInstitute of Physics, Cz¸estochowa University of Technology, 42–200 Cz¸estochowa, Poland, E–mail: [email protected] bWroclaw University, Institute of Experimental Physics, 9 Max Born Sq., 50–204 Wroclaw, Poland

The crystal structure of dimethylammonium gallium sulfate hexahydrate (DMAGS) and the isomorphic dimethyloammonium aluminium sulfate hexahydrate (DMAAS) is build up of Ga or Al cations, coordinating six water molecules, regular SO4 tetrahedra + and [(CH3)2NH2] (DMA) cations, all hydrogen bonded to a three dimentional framework. Both crystals are ferroelastic in paraelectrics phase with space group P21/n. Both of them exhibit an order-disorder type transition into a ferrelectric phase at TC1 = 134 K and TC1 = 152 K, respectively. Additionally, only DMAGS shows a further first order transition into a low temperature non-ferrelectric phase at TC2 = 116 K. The reason for this different behavior of DMAAS and DMAGS in not yet fully understood. In the present communication paper we report on EPR measurements of chromium doped DMAAS and DMAAGS performed in the X-band (9.5 GHz) in the wide temperature range from room temperature down to liquid helium temperature. The rotation pattern of the spectra show in paraelectric and the ferroelectric phase two magnetically equivalent sets of lines in accordance with two chemically equivalent Al and Ga sites in unit cell, which can be substituted by Cr3+ ions. In both crystal a strong broadening and next a line tripling is observed already in ferroelastics phase far above TC1. The observed broadening disappear and lines narrow drastically in ferroelectric phase on lowering the temperature. These linewidth changes confirm the order-disorder character of the ferroelectric phase transition. At T > TC1 DMA groups are dynamically disordered, executing random flips around the axis connecting the two methyl oxygens. The amino group form two ones with different probability which manifests by tripling of EPR lines mentioned above. In DMAGS at the temperature TC2 = 116 K transition into the non-ferrelectric low-temperature phase is accompanying by large spectrum changes. Lowering the temperature further on, below TC3 = 64 K the spectrum sim- plifies considerably having much narrow lines but the number of these lines is doubled in comparison to the paraelectric and ferroelectric phases.

38 Tuesday, September 5 L 17

EPR of the Gd3+ probe near ferroelectric phase transition in Pb5Ge3O11 M.P. Trubitsyna, S. Waplakb and Yu.D. Krokhmal’a aDepartment of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, 49050 Dnipropetrovsk, Ukraine, E–mail: trub@ﬀ.dsu.dp.ua bInstitute of Molecular Physics, Smoluchowskiego 17/19, 60–179 Pozna´n, Poland, E–mail: [email protected]

In the numerous investigations of the physical properties near structural phase transitions (SPT) it is assumed that critical fluctuations are responsible for deviations from the classical mean field theory. In that way the experimental results are described by power laws with non-classical critical exponents predicted by the universal models with short-range forces. However in the crystalline systems undergoing SPT, the long- range elastic interactions are essential that favours the mean field approximation. In fact using of the simple power relations in many cases oversimplifies the real situation and the experimental data can be described even within mean field approach with accounting of the order parameter coupling with another degrees of freedom, presence of the structural defects, etc. An argued choice of the way to interpret the experimental data needs detailed analysis in each concrete case. The critical interval around SPT may be estimated with the help of Ginzburg- Levanyuk (GL) criterion. Since the GL criterion is not universal and obtained estima- tions depend on the properties studied, the most direct way seems to compare order parameter (OP) value with mean square fluctuation. In that case using of the magnetic resonance (MR) spectroscopy gives noticeable advantages. Really studying of the MR line splitting below SPT point allows to measure local OP value, whereas MR line width broadening around TC reflects anomalous growth of the local OP fluctuations. Comparison of the MR line splitting with line width broadening should indicate the temperature interval around TC where OP fluctuation exceeds OP value. The given arguments are illustrated with the EPR spectra studying in the lead 3+ germanate Pb5Ge3O11 crystals doped with Gd probe. It is shown that the reduced ∗ −2 temperature restricting the critical region is τGL = T −TC /TC ≈ 2·10 and deviations from the phenomenological theory may be expected in a broad enough temperature interval.

39 L 18 Tuesday, September 5

Phase transitions in KDP crystals with the complex organic and inorganic impurities

B. Strukov, I. Shnaidshtein and S. Grabovsky Lomonosov Moscow State University, Vorob’evi Gori, 119992 Moscow, Russia, E–mail: [email protected]

The proximity of ferroelectric phase transition in KDP crystals to a tricritical point as well as its piezoelectric activity above Tc result in the essential contraction of the temperature region where the polarization fluctuation can be visible. For this reason KDP crystals are the very attractive objects for study of the effects of impurities upon the phase transition anomalies. It was shown several decades ago that the crystal matrix of KDP can incorporate the large non-isomorphic organic dye molecules. Recently it was shown that there are a lot of the dye molecules having similar property and the different dyes can be incorporated only into certain growth sectors of the crystal. Such kind of “recognition” is typical also for some inorganic dyes with a complex molecular structure; therefore organic dye Amaranth (A) and Chicago Sky Blue (CSB) stain only pyramidal sectors while Xylenon Orange (XO), Hematein and inorganic Pento-Chloro- Ruthenate (PCR) stain only prismatic sectors. Dielectric and thermal study of the KDP crystals for stained and achromatic zones in comparison with the pure crystal are presented for the very vicinity of the phase transition as well as for the wide temperature interval. The displacement of the transition point, smearing of the transition, variations of the domain contribution to the dielectric constant in polar phase are analyzed for all the kind of impurities. The formation of the biasing field and arising of the metastable states (“polarization back to the field”) are revealed and discussed. It is found that the unstained prismatic sectors of A – KDP occurred to be quite pure from the usual background impurities (ions of trivalent metals). The high-resolution specific heat data for this part of the crystal reveal the effect of splitting of the specific heat anomaly maximum which was described in the framework of Landau theory using the model of the random field type defects. The possible models of incorporation of the complex molecules into KDP structure are proposed. This work was supported by RFBR (project 05-02-16873-a).

40 Tuesday, September 5 L 19

Thermodynamics and relaxation dynamics of the Rb1−x(NH4)xH2PO4 type proton glasses R.R. Levitskiia, S.I. Sorokova, Z. Trybulab and A.S. Vdovycha aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bInstitute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60–179 Pozna´n, Poland

For description of thermodynamic and dielectric properties of the Rb1−x(NH4)xH2PO4 type proton glasses a pseudospin model with competing short- range and long-range interactions and random internal fields was proposed [1]. Within a symmetric replica approach, the four-particle cluster approximation for the short-range interactions and the mean field approximation for the long-range interactions are used. The system of equations for distribution function of static effective fields of hydrogen bonds is derived and Gauss solutions are obtained. Ferroelectric and proton-glass order parameters are investigated, and static phase diagrams for Rb1−x(NH4)xH2PO4, K1−x(NH4)xH2PO4, K1−x(ND4)xD2PO4 systems are constructed. A good description of experimental data for the transition lines to ferroelectric phase, to antiferroelectric phase, and for the freezing line in central region of x (transition from an ergodic proton-glass to a non-ergodic proton-glass) is obtained. Within the Glauber kinetic approach, the system of equations for distribution function of static effective fields and dynamic linear response of effective fields within the cluster approximation are derived and Gauss solutions are obtained. The temperature dependence of the transverse dynamic permittivity and effective relaxation time is studied for the mentioned above compounds at different x. Arrhenius behavior of the relaxation time is obtained. In a wide region of concentrations x, the theoretical freezing lines are close to experimental data [2]; in the central region of x the static freezing line (inflection point of static permittivity) coincides with the dynamic freezing line (maximum of the imaginary part of the dynamic permittivity). The discrepancy between the behavior of the theoretical freezing line and the experimental data at x → 0 and x → 1 is discussed.

1. R.R. Levitskii, S.I. Sorokov, A.S. Vdovych. Condens. Matter Phys., 2005, v. 8, No. 3(43), p. 603–622. 2. Z. Trybula, V.H. Schmidt, J.E. Drumheller. Phys. Rev. B, 1991, v. 43, No.1, p. 1287.

41 L 20 Tuesday, September 5

Critical behaviour of the susceptibility and heat capacity of the 3D Ising systems at the presence of an external ﬁeld

M. Kozlovskii Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

The method for the calculation of the partition function of the Ising model in an external field near the critical point is proposed. The critical point of the 3D one- component spin system is defined. The critical behavior of the system at h = 0 has been studied on the microscopical level [1]. We also know some characteristics for the 3D model at T = Tc with the external field tending to zero. The details of critical behavior of the 3D system are still unclear in general case when T → Tc and h → 0. For this case, we develop an approximate method for the description of the one-component 3D model near the phase transition point. This method is based on the microscopic theory of phase transitions [1]. It uses the collective variables set containing the variable, which corresponds to the order parameter of the system. The introduction of external field leads to a more general description of critical behavior. The analytic explicit expressions for the free energy, average spin moment, specific heat and susceptibility are obtained for the case of T > Tc. The calculations are performed on the microscopic level without any adjusting parameters.

1. I.R. Yukhnovskii, M.P. Kozlovskii, I.V. Pylyuk, Microscopic Theory of Phase Transi- tion in the Three-Dimensional Systems (Eurosvit, Lviv. 2001. – 592 p.) [in Ukrainian].

42 Tuesday, September 5 L 21

Studies of transfer phenomena in Li2B4O7 N.D. Baysaa, I.M. Rizakb, V.S. Bilanychc, Z. Trybulad, V.M. Holoveye and V.M. Rizakc aNational Aviation University, Kyiv, Ukraine bDnipropetrovsk National University, Dnipropetrovsk, Ukraine cUzhgorod National University, Uzhhorod, Ukraine, E–mail: [email protected] dInstitute of molecular physics of the Polish academy of sciences, Poznan, Poland eInstitute of Electron Physics NAS of Ukraine, Uzhhorod, Ukraine

Lithium tetraborate Li2B4O7 (LTB) single crystals possess a complex of physical properties of special interest for their practical applications in radiative physics, nonlinear optics and acoustooptics. Dynamics of the change of physical parameters of the LTB-based active media is mainly due to the condition of structural subsystems. In this paper, the results of the studies of transfer phenomena in pure and Mn-doped LTB crystals are presented. To study the above phenomena we have investigated heat and electric conductance and internal friction in the LTB crystals. Heat conductance was measured by using the dynamical linear heating method within the 4–300 K temperature range. Electrophysical characteristics were measured using the automated setup allowing the active and reactive conductance components to be detected within the 293–1380 K temperature range and the 103–106 Hz frequency range. Specimen heating rate was 2 k/min. Internal friction was measured in the quasistatic regime at the 10−3–10−1 Hz frequencies using the torsion vibration method. As the analysis of electric conductance in the pure and doped LTB has shown that ln(σT ) = F (1/T ) dependences are well approximated by straight lines with different slope angle. Mn doping affects considerably the charge transfer only in the temperature range T < 800 K. The temperature dependences of tg δ in the LTB single crystal within the 400–600 K temperature range reveal a maximum, the position of which depends on the frequency. Doping this crystal results in an additional maximum indicating the appearance of additional positions for ion leap at the charge transfer. Dominating ionic conductance was analyzed within the framework of the dielectric cation relaxation model in the intersite positions along the conductance channels. The minimal length of the Li+ cation leap and the height of the potential barrier between their closest positions have been determined. The temperature spectrum of the internal friction in the LTB crystal reveals an amplitude-dependent maximum allowing, using its parameters, to determine the particle, which stipulates this dissipative process. It has been shown that this process could be due to the lithium ion migration between the energetically equivalent positions under the influence of alternating external field.

43 L 22 Wednesday, September 6

Rotation degree of freedom for the motion of glycine molecule

J. Stankowski Institute of Molecular Physics Polish Academy of Sciences, 17 M. Smoluchowskiego Str., 60–179 Pozna´n, Poland

Abstract was not available at printing time.

44 Wednesday, September 6 L 23

Correlation between DSC and non-linear optical monitoring of the phase transitions

M. Piasecki, I.V. Kityk and K. Ozga Institute of Physics, J. Dlugosz University Czestochowa, Al. Armii Krajowej 13/15, Czestochowa, Poland, E–mail: [email protected]

Comparison of the monitoring of the phase transitions performed by the DSC and non-linear optical methods is carried out following the complex experimental investigations performed for different material possessing phase transitions: glasses, crystals, nanocomposites, ferroelectrics. It was established that the maximum of the photoinduced SHG coincides with the maximum DSC temperature derivative of the investigated material. Influence of the cooling-heating rates are discussed together with observation of the temperature hysteresis. Specific requirements to the experimental set-up and to the sample preparation are given. Physical aspects of the phenomena are discussed within the framework of the phenomenological approach. Particular attention is devoted to the thermocycling and to the critical indices of the corresponding temperature dependences.

45 L 24 Wednesday, September 6

Combined crystalooptical eﬀects in ferroelectrics and ferroelastics

R. Vlokh and O. Mys Institute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine, E–mail: [email protected]

Combined crystallooptical effects consist in the change of the real or imagine refractive indices of crystals at the common action of the fields of different nature. Present report is devoted to experimental study of piezo-electrooptical effect in LiTaO3, LiTaO3, Pb5Ge3O11, Ca2Pb(C2H5CO2)6 ferroelectric crystals and K2Cd2(SO4)3 ferroelastic crystals in particular at the phase transition. The behaviour of the coefficients of these effects at phase transition is obtained and discussed in the frame of Landau theory. It has been shown that combined crystallooptical effects can be efficiently used at improvement of laser radiation control.

46 Wednesday, September 6 L 25

Investigation of ferroelectric-antiferroelectric mixed compounds

N.A. Korynevskiia,b and V.B. Solovyana aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bInstitute of Physics, University of Szczecin, 15 Wielkopolska Str., 70451 Szczecin, Poland

The statistical model [1] for ferroelectric-antiferroelectric mixed hydrogen bonded compounds is analyzed in details. On the base of obtained phase diagram “concentration-temperature” the possible types of order parameters in mixed system are founded. It was shown that long order parameters (polarization and antipolarization) are realized either in “right” or in “left” sides of phase diagram and the areas of their existence never cross each other [2]. The dipole glass phase, which takes place at low temperatures for intermediate values of concentration, is described by the complex non-uniform behavior of the pair correlation function of nearest neighbors. The detailed temperature and concentration dependencies of dipole glass order parameters are founded.

1. Korynevskii N.A., Baran O.R. Ferroelectrics, 2004, 300, 151. 2. Korynevskii N.A., Solovyan V.B. Reviews of Advanced Material Science, 2006, 12, 90.

47 L 26 Wednesday, September 6

Landau-Ginzburg theory of phase transitions on fractal systems

Z. Bak Institute of Physics, JD University of Czestochowa, Al. Armii Krajowej 13/15, 42–201 Czestochowa, Poland, E–mail: [email protected]

The concept of fractal has become a powerful tool in analysis of common aspects of many complex processes observed in physics, biology, chemistry or earth sciences. Brownian motion, turbulence, colloid aggregation or biological pattern formation can be fully understood only when the idea of self-similarity or fractal structures is applied. The fractals can be realized in nature as the fractal process or a fractal medium. The hallmark of a fractality is a hierarchical organization of its elements, described by dis- crete scaling laws which makes the fractal, regardless on magnification or contraction scale looks the same, this property of fractals is called self-similarity or self-affinity or self-replicability. Typical examples of fractal systems are dipole electric/magnetic patterns (clusters) on a solid surface. In our contribution we give phenomenological description of phase transition of fractally structured systems or those that exhibit fractional dimensionality (see e.g. [1]). Physical systems modeled by fractals are inho- mogenous, thus any description in terms of mean-field approximation is no longer valid. However, we show that for some class of fractal systems by transition to the logarithmic scale coordinates we are able to restore the translational symmetry in mass, electric dipole or magnetic moment distribution. This opens possibility to describe the phase transition of self-similar fractals in the way that is reminiscent of conventional formalism developed for crystalline systems. Motivated by this fact we present the study of phase transitions on fractal systems, which is a generalization of the conventional Landau-Ginzburg model. We prove that, when compared to earlier approaches [2–3] to the problem, our model is much simpler and can be easily extended onto fractal processes that exhibit log-periodic modulations.

1. Z. Bak, Phys. Rev. 68B, 064511 (2003). 2. A.V. Milovanov, J.J. Rasmussen, Phys. Lett. A 337, 75 (2005). 3. V.E. Tarasov, G.M. Zaslavsky, Physica 354A, 249 (2005).

48 Wednesday, September 6 L 27

Pyroelectric and ferroelectric hysteresis in the ferroelectric-semiconductor ﬁlms with charged defects

A.N. Morozovskaa, E.A. Eliseevb, D. Remiensc and C. Soyerc aV. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, 41 Nauki Ave., 03028 Kiev, Ukraine, E–mail: [email protected] bInstitute for Problems of Materials Science, National Academy of Science of Ukraine, 3 Krjijanovskogo Str., 03142 Kiev, Ukraine, E–mail: [email protected] cIEMN, UMR 8520 OAE-dept/ MIMM, Universite de Valenciennes et du Hainaut-Cambresis, Le Mont Houy, 59313 Valenciennes Cedex 9, France

We have modified Landau-Khalatnikov approach and shown that both the polar lattice and the screened charged defects determine the response of disordered ferroelectric- semiconductor films. We have shown that the ferroelectric and pyroelectric response of inhomogeneous ferroelectric-semiconductor films can be described by using six coupled equations for six order parameters: average displacement, its mean-square fluctuation and correlation with charge defects density fluctuations, average pyroelectric coefficient, its fluctuation and correlation with charge defects density fluctuations. Coupled equations demonstrate the inhomogeneous reversal of pyroelectric response in contrast to the equations of Landau-Khalatnikov type, which describe the homogeneous reversal with the sharp pyroelectric coefficient peak near the thermodynamic coercive field value. Within the framework of our model pyroelectric hysteresis loop becomes much smoother, thinner and lower as well as pyroelectric coefficient peaks near the coercive field completely disappear under the increase of disordering caused by defects. This effect is similar to the well-known “square to slim transition” of the ferroelectric hysteresis loops in relaxor ferroelectrics. Also the increase of defect concentration leads to the drastic decrease of the coercive field typical for disordered ferroelectrics. Our model gives more realistic pyroelectric hysteresis loop shape without any peaks near the coercive field and describes both qualitatively and quantitatively typical Pb(Zr,Ti)O3 and (Sr,Ba)Nb2O6 films pyroelectric hysteresis loops.

49 L 28 Thursday, September 7

Pyroelectric electron and X-ray generator – a review

B. Koniecznaa, M. Cichab and K. Biedrzycki aUniversity of Wroclaw, Institute of Experimental Physics, Maxa Borna 9, 50–204 Wroclaw, Poland bUniversity of Zielona G´ora, Institute of Physics, Szafrana 4a, 65–516 Zielona G´ora, Poland cUniversity of Opole, Institute of Physics, Oleska 48, 45–052 Opole, Poland

Pyroelectricity is a phenomenon resulting from a permanent electric dipole in the primitive unit cell of a crystal in thermal equilibrium. This phenomenon is observed in some class of crystals with polar symmetry axis, e.g. linear polar dielectric and ferroelectrics, and is manifested by the presence of transient surface charge in response to a change of temperature. It is well known that a lot of application of pyroelectric materials for infrared detection, power conversion, memories, etc. have been found. In a proposed talk a new area of application of pyroelectric materials as a source of electrons and X-rays with energies up to a few tens of keV, developed during the last thirty years, are presented and discussed.

50 Thursday, September 7 L 29

Magnetoelectric multiferroics: present-day reality and promises

M. Kharchenko Institute for Low Temperature Physics and Engineering, NASU, 47 Lenin ave., 61103 Kharkiv, Ukraine, E–mail: [email protected]

A few last years an exponential rapidly growing interest to magnetic ferroelectrics (magneto-electrical multiferroic materials), in which electrical and magnetic subsystems strongly interact with each other is observed. The magnetoelectric coupling gives possibilities to vary magnetic properties by means of an electric field and vice versa. Recently the reorientation of electric polarization by magnetic field, and the switching of magnetic states by electric field were observed. Besides the colossal influence of a magnetic field on the dielectric permittivity (magneto-capacitance) near the phase transition was revealed. The magnetoelectric coupling is usually weak, but among different mechanisms responsible for its formation there are also those (in noncollinear magnetic structures), which provide strong coupling between the certain magnetic and electrical order parameters. Due to these mechanisms the certain magnetic ordering causes ferroelectricity and vice versa. Simultaneously broken space-inversion and time-reversal symmetry in magnetoelectric ferroics give rise to the new non-reciprocal optical, magnetoelectrooptical effects. These effects are usually small and some of them are so small that it is difficult to observe experimentally. But the effects can be enhanced by some orders by use of the periodic arrays in the photonic crystals composed of magnetoelectric multiferroic materials. The brief review of recent investigation results of the magnetoelectric multiferroics is submitted in the report.

51 L 30 Thursday, September 7

Role of piezoelectricity in relaxational and other dynamical properties of ferroelectrics

R.R. Levitskiia, I.R. Zachekb, A.P. Moinaa and A.S. Vdovycha aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine bLviv Polytechnical National University, 12 Bandery Str., 79013 Lviv, Ukraine

A goal of this work is to elucidate the role of piezoelectric interactions on the thermodynamics, physical characteristics, dynamic relaxational and piezoelectric resonance phenomena, as well as sound attenuation in ferroelectric crystals of Rochelle salt and KH2PO4. Calculations for deuterated KH2PO4 type crystals are performed within the four- particle cluster approximation for the proton ordering model with taking into account a coupling with the shear strain ε6. A mean field approximation for the modified two- sublattice Mitsui model with piezoelectric coupling with the shear strain ε4 is used for Rochelle salt crystals. Dynamics of the spin subsystem in both types of crystals is considered within the Glauber approach, and it is supplemented with the Newtonian dynamics of the shear strain. Expressions for the dynamic dielectric permittivity, elastic stiffness and piezoelectric moduli, as well as sound velocity and attenuation of the crystals are derived. A thorough numerical analysis of the obtained results is performed; sets of the theory parameters providing a satisfactory description of the corresponding experimental data are found. It is shown that the influence of piezoelectric coupling on spontaneous polarization and specific heat of the crystals is minor. However, the character of the temperature and frequency dependences of the dynamic dielectric characteristics of the crystals are essentially affected by their piezoelectricity. The effects include the crystal clamping by the high-frequency electric field and piezoelectric resonances. A detailed comparison of the piezoelectricity role in the KH2PO4 type crystals, undergoing a single first order phase transition and in Rochelle salt, undergoing two second order phase transitions is made.

52 Thursday, September 7 L 31

Anisotropy of laser-induced bulk damage of single crystals

O. Krupych, Ya. Dyachok, I. Smaga and R. Vlokh Institute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine, E–mail: [email protected]

The regularity of laser-induced damage of anisotropic media, such as β-BaB2O4, LiB4O7, LiNbO3 and KDP dielectric single crystals was experimentally studied. It was observed that the shape of laser-induced damage of dielectric single crystals depends on the crystal elastic symmetry and the laser irradiation direction. Figures of laser damage when laser beam propagates along optical axis of crystals are four-path stars for KDP, six-path stars for β-BaB2O4 and LiNbO3 and eight-path stars for LiB4O7 crystals. On the base of extension factor indicative surfaces analysis, it was shown that cracks are perpendicular to the directions of minimal values of extension factor. When laser irradiation was directed along X- and Y -axis of KDP crystal, damage had initially cross-like conﬁguration with splitting of Z-oriented crack on two cracks at damage evolution that lead to transformation of orthogonal-type damage to hexagonal-type.

53 L 32 Thursday, September 7

Borate crystals – new high eﬃcient acoustooptic materials

I. Martynyuk-Lototskaa, O. Mysa, O. Krupycha, V. Adamiva, Ya. Buraka, R. Vlokha, O. Vlokha and W. Schranzb aInstitute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine, E–mail: [email protected] bInstitut f¨ur Experimentalphysik, Universit¨at Wien, 1090 Wien, Austria

The refractive, elastical and piezooptical properties of the borate crystals (β- BaB2O4 – BBO, α-BaB2O4 – ABO, Li2B4O7 and CsLiB6O10) have been studied as well as optical damage threshold and range of transparency. The photoelastic coefficients of ABO, BBO, and LiB4O7 crystals where calculated on the base of measured by interferometric technique piezooptical coefficients and elastic compliances and stiffness. On the base of experimentally obtained data the acoustooptical figure of merit has been estimated for possible geometries of acoustooptical interaction. It was shown that acoustooptical figure of merit of ABO, BBO and Li2B4O7 crystals achieve value −15 3 −15 3 −15 3 M2 = 243 · 10 s /kg, M2 = 49 · 10 s /kg and M2 = 2.6 · 10 s /kg, respectively at the interaction with the slowest ultrasonic waves. The direction of propagation and polarization of these acoustical waves were obtained by construction of the indicative surfaces of acoustic waves velocities. The acoustooptical diffraction in the Li2B4O7 and ABO crystals was experimentally observed. The optical damage threshold of these crystals was experimentally determined and achieves values for Li2B4O7 2 2 2 crystals – 32.2 GW/cm , BBO – 30.9 GW/cm , CsLiB6O10 – 7.5 GW/cm , ABO – 14.5 GW/cm2 and ABO doped by Sr – 59 GW/cm2. The range of transparency for Li2B4O7 crystals is 250–3200 nm, BBO – 280–3220 nm, CsLiB6O10 – 250–2800 nm and ABO – 250–3200 nm. It was shown that borate crystals are perspective material for acoustooptical application for superpower laser radiation in wide spectral range.

54 Thursday, September 7 L 33

Polarization relaxation in non-uniform ferroelectric crystals

R.Z. Rogowski and K. Matyjasek Institute of Physics, Szczecin University of Technology, Al. Piastow 48, 70–310 Szczecin, Poland, E–mail: [email protected]

The characteristic features of polarization and spontaneous depolarization kinetics in non-uniform telluric acid ammonium phosphate (TAAP) crystal were investigated by observation of the domain structure using nematic liquid crystal method. We present experimental results showing the correlation between the internal bias field, responsible for the offset of the hysteresis loop and the backswitching process. The internal field caused by structural disorder accounts for a broad spectrum of energy barriers for domain nucleation. On the assumption that relaxation centers do not interact, probable spectra of the distribution of the characteristic domain growth times are derived from the experimental data.

55 L 34 Thursday, September 7

Metal-insulator like transition in energy spectrum of one-dimensional proton (ionic) conductor

I.V. Stasyuk and O. Vorobyov Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

Recently various systems with proton (ionic) conductivity are extensively investigated. A lot of attention is paid to so-called superionic conductors, e.g. MeH(XO4) and Me3H(XO4)2, where Me is Cs, Rb, NH4 and X is Se or S. The low temperature phases of these crystals are ferroelectric or ferroelastic while the high temperature phase is superionic. In superionic phase the conductivity arises due to the motion of protons in the two-dimensional or one-dimensional networks of hydrogen-bonded ionic groups. We focus on the simpler one dimensional case. We describe the one-dimensional proton conductor with the lattice fermion model that takes into account the proton transfer in the spirit of two-stage Grotthuss mechanism as well as the interactions between nearest protons. Also this model can be easily simplified to well-known spinless fermion model which is suitable for the description of the systems with ionic conductivity. We develop the approach based on the well-known coherent potential approximation (CPA) which is modified to include short-range interactions of protons (ions) into consideration. In frames of this approach we calculate the proton energy spectrum at various values of system parameters. At weak interaction strength the spectrum consists of one band at any concentration of protons (ions). At strong interactions the spectrum is split into several energy bands. In this case the proton (ion) subsystem can be in either quasi-metallic or insulating state depending on average concentration of protons. Moreover, at some values of interaction constatnts the system undergos metal-insulator like transition at half-filling (one proton per hydrogen bond or 1/2 ions per site) with the change of temperature.

56 Thursday, September 7 L 35

Speciﬁc features of optical absorption processes in IV V VI A2 B2 C6 ferroelectrics A.G. Slivka, I.P. Studenyak, O.O. Gomonnai, I.Yu. Kuritsa and P.P. Guranich Uzhhorod National University, Optics Department, 54 Voloshyn Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected]

Experimental results on the temperature behaviour of fundamental optical absorption spectra of Sn(Pb)2P2S(Se)6 crystals and solid solutions on their base are analyzed in the framework of Cody-Einstein theoretical model. Contributions of temperature-related dynamic and structural static disordering to the absorption edge energy width of the crystals are determined and their variation at phase transitions from ferroelectric to paraelectric phase. The calculated temperature dependences of the energy gap are compared with the results of direct experimental measurements.

57 L 36 Thursday, September 7

Radiochromic phenomena in the ferroics with transition metal ions

V.B. Kapustyanyk and V.P. Rudyk Ivan Franko National University of Lviv, Scientiﬁc-technical and Educational Center of Low Temperature Studies, 50 Dragomanova Str., 79005 Lviv, Ukraine, E–mail: [email protected]

The transition metal ions with their strong coupling to the surrounding ligands are convenient probes for investigations of the radiation effects in crystals. The electronic and vibration spectra of corresponding complexes appeared to be very sensitive to the bare changes of a crystalline structure caused by ionizing irradiation. The investigated crystals could be very attractive for application in the sensors of radiation. The first order phase transition (PTs) were observed in (NH2(C2H5)2)2CuCl4 crystals grown from the alcohol (DEACC-I) and water solution (DEACC-II). Their clear thermochromic nature is connected with an abrupt change of the copper ion environment from tetrahedral to the square planar. The hydrogen bonds N–H. . . Cl are involved into this process. Due to this the compounds of such a type manifest a clear radiochromic effect which consists in the shift of the temperature of the first order thermochromic PT induced by ionizing radiation. The crystals of NH2(CH3)2Al(SO4)2 · 6H2O doped with chromium (DMAAS:Cr) have been widely studied recently using different experimental methods. They show a complicated sequence of PTs into the ferroelectric (Tc1 = 154 K) and obviously into the antiferroelectric phases (T2 = 75 K) respectively. It was found that comparatively low doses (≈ 0.5 R) of ionizing radiation first of all cause recharging of Cr3+ to Cr4+ and Cr2+ states obviously with formation of the localized exciton states. On the other hand, the processes of dehydrogenation occur in result of irradiation. Moreover, the changes in the arrangement of the hydrogen bond network are observed that leads to the distortion of the complexes bonded by such a type of bonds. All observed effects are found to be practically reversible although for the full returning of the sample toward the pre-radiation state at least thirty days are necessary. The chromium ion recharging was also observed as a true time process at immediate irradiation of a sample. The dynamics of above mentioned effects was analyzed by the oscillator strength of the absorption bands corresponding to the Cr3+, Cr4+ and Cr2+ ions.

58 VIII Ukrainian-Polish and III East-European Meeting

on Ferroelectrics Physics

Posters

4–7 September 2006, Lviv, Ukraine

VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

Tuesday, September 5, 2006 Afternoon Sessions 15:00 – 19:30 Session IX Poster Session Chaired by I.V. Stasyuk, Z. Czapla, D. Michel and Yu.M. Vysochanskii

1. B. Andriyevskya, W. Ciepluch-Trojaneka, A. Patryna, N. Esserb, C. Cobetb and M.M. Romanyukc Band structure and optical spectra of ferroelectric triglycine sulfate aKoszalin University of Technology, Koszalin, Poland bISAS – Institute for Analytical Sciences Department Berlin, Berlin, Germany cIvan Franko National University of Lviv, Faculty of physics, Lviv, Ukraine 2. B. Andriyevsky, W. Ciepluch-Trojanek and A. Patryn Influence of hydrostatic pressure on structural and electronic parameters of TGS crystals (first-principal calculations) Koszalin University of Technology, Koszalin, Poland 3. R.R. Levitskiia, I.R. Zachekb, A.Ya. Andrusyka and I.V. Kutnyc Theoretical investigation of the thermodynamic and dynamic properties of the crystals with asymmetric double-well potential within the framework of the Mitsui model taking into account tunnelling effects and piezoelectric interaction aInstitute for Condensed Matter Physics, Lviv, Ukraine bNational University “Lviv Polytechnic”, Lviv, Ukraine cLviv Commercial Academy, Lviv, Ukraine 4. R.R. Levitskiia, A.P. Moinaa, I.R. Zachekb, A.Ya. Andrusyka, A.G. Slivkac and V.M. Kedyulichc Investigation of the hydrostatic pressure influence on the phase transitions and physical properties of the Rochelle salt and RbHSO4 crystals aInstitute for Condensed Matter Physics, Lviv, Ukraine bLviv Polytechnical National University, Lviv, Ukraine, cUzhgorod National University, Uzhgorod, Ukraine 5. D.M. Berchaa,b, L.Yu. Kharkhalisa, I.V. Slipukhinaa and M. Sznajderb Elementary energy bands concept in IV-VI crystals with phase transitions aInstitute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine bInstitute of Physics, University of Rzeszów, Rzeszów, Poland

61 4–7 September 2004, Lviv, Ukraine

6. K.V. Bodnar, A.A. Grabar, I.V. Kedyk, Yu.Yu. Gaza, M.M. Danko, L.S. Gaza and Yu.M. Vysochanskii Optical and photoelectric parameters of doped Sn2P2S6 ferroelectric crystals Institute for Solid State Physics and Chemistry of Uzhgorod National University, Uzhgorod, Ukraine 7. K. Cwikiel´ a and E. Nogas-Cwikiel´ b Dielectric and pyroelectric properties of the Ba0,3Na0,7Ti0,3Nb0,7O3 ceramics obtained by sol-gel method aUniversity of Silesia, A. Chelkowski Institute of Physics, Katowice, Poland bUniversity of Silesia, Faculty of Computer Science and Materials Science, Sosnowiec, Poland 8. S. Dacko, Yu. Eliyashevskyy and Z. Czapla Dielectric properties of [(CH3)2NH2]3CuCl5 in external electric field Wroclaw University, Institute of Experimental Physics, Wroclaw, Poland 9. V.M. Duda and T.V. Kruzina Protonation and conductivity of Na0.5Bi0.5TiO3 ceramics at high temperature Department of the solid state physics, Dnipropetrovsk National University, Dnipropetrovsk, Ukraine 10. V.M. Duda, A.S. Ermakov, V.G. Linnik and A.S. Belous Nonstoichiometry and conductivity of Pb5Ge3O11 single crystals Department of the solid state physics, Dnipropetrovsk National University, Dnipropetrovsk, Ukraine 11. E.A. Eliseeva, M.D. Glinchuka and A.N. Morozovskab Antiferroelectric thin films phase diagrams aInstitute for Problems of Materials Science, NAS of Ukraine, Kiev, Ukraine bV. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Kiev, Ukraine 12. Yu. Eliyashevskyya, A. Sieradzkib, R. Poprawskib and Z. Czaplaa Influence of the hydrostatic pressure on phase transitions of [(CH3)2NH2]3CuCl5 crystals aWroclaw University, Institute of Experimental Physics, Wroclaw, Poland bWroclaw University of Technology, Institute of Physics, Wroclaw, Poland 13. B. Garbarz-Glosa, W. Smiga´ a, J. Suchanicza, D. Sitkoa, M. Dambekalneb, A. Sternbergb and D. Skolyszewski a Synthesis, microstructure and dielectric properties of (1 − x)PSN–xPLuN aInstitute of Physics, Pedagogical Academy of Krakow, Poland bInstitute of Solid State Physics, University of Latvia, Latvia

62 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

14. A.V. Gomonnai Raman scattering in macro- and mesoscopic Sn2P2S6 ferroelectrics Institute of Electron Physics, Ukr. Nat. Acad. Sci., Uzhhorod, Ukraine

15. A. Hek, S. Dacko and Z. Czapla Dielectric investigation of 2-aminopyridyne phosphate crystal Wroclaw University, Institute of Experimental Physics, Wroclaw, Poland

16. V. Holovatsky and V. Gutsul Electron energy spectrum in core-shell elliptic quantum wire Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, Chernivtsi, Ukraine

17. I. Katerynchuka, S. Svelebaa, O. Semotyuka, I. Kunyoa and Yu. Pankivskyib The temperature – time eﬀects in the incommensurate phase of [N(CH3)4]2CuCl4 and [N(CH3)4]2ZnCl4 crystals aDepartment of Nonlinear Optics, Lviv National University, Lviv, Ukraine bDepartment of Ecology, National University of Forestry, Lviv, Ukraine

18. V.M. Kedyulich, H.M. Guyvan and A.G. Slivka Eﬀect of external pressure and electric ﬁeld on the dielectric properties of Rochelle salt Uzhhorod National University, Optics Department, Uzhhorod, Ukraine

19. Yu. Kharchenko Birefringence of the linearly polarized light in the magnetoelectric single crystal LiNiPO4 Institute for Low Temperature Physics and Engineering, NASU, Kharkiv, Ukraine

20. V. Khrustalyov, V. Savitsky and M. Kharchenko High-ﬁeld magnetization of magnetoelectric antiferromagnet LiCoPO4 Institute for Low Temperature Physics and Engineering, NASU, Kharkiv, Ukraine

21. K. Konieczny, W. Smiga,´ B. Garbarz-Glos, G. Stopa and Cz. Ku´s Pyroelectric study of Na1−xLixNbO3 ceramic Institute of Physics, Pedagogical University, Krakow, Poland

22. A.V. Konstantinovich and I.A. Konstantinovich The radiation spectrum of an electron moving in a spiral in medium Chernivtsi National University, Department of Theoretical Physics, Chernivtsi, Ukraine

63 4–7 September 2004, Lviv, Ukraine

23. B. Kostureka, A. Wa´skowskab, S. Dackoa and Z. Czaplaa Structure and phase transition in pyridazine perchlorate aWroclaw University, Institute of Experimental Physics, Wroclaw, Poland bPolish Academy of Sciences, Institute of Low Temperature and Structural Research, Wroclaw, Poland

24. V.M. Duda, T.V. Kruzina, V.G. Pozdeev and S.A. Popov Phase transitions in Na0.5Bi0.5TiO3–BaTiO3 crystals Department of the solid state physics, Dnipropetrovsk National University, Dnipropetrovsk, Ukraine

25. O.S. Kushnir and R.Y. Shopa Combined studies for the ferroelectric phase transition in deuterated triglycine sulfate Electronics Department, Ivan Franko Lviv National University, Lviv, Ukraine

26. I.E. Lipinski´ a, J. Kuriataa and N.A. Korynevskiib,c On a correlation between EPR data for SASeD doped with Cr3+ and soft modes aInstitute of Physics, Szczecin University of Technology, Szczecin, Poland bInstitute for Condensed Matter Physics, Lviv, Ukraine cInstitute of Physics, University of Szczecin, Szczecin, Poland

27. B.M. Lisnii, R.R. Levitskii and O.R. Baran Inﬂuence of the electric ﬁeld E3 and the shear stress σ6 on the ferroelectric phase transition in the KH2PO4 crystal Institute for Condensed Matter Physics, Lviv, Ukraine

28. M.M. Maior, I.P. Prits, I.I. Makauz and Yu.M. Vysochanskii Dielectric and piezoelectric response of GeS2–Sn2P2S6 glass ceramics Institute of Physics and Chemistry of Solid State, Uzhgorod University, Uzhgorod, Ukraine

29. M. Maior, L. Beley, M. Gurzan, N. Korda and Yu.M. Vysochanskii Dielectric susceptibility of CuInP2(SexS1−x)6 ferroelectrics: does a dipole glass state exist on their phase diagram? Institute of Physics and Chemistry of Solid State, Uzhgorod University, Uzhgorod, Ukraine

30. O. Makhanets, A. Gryschyk and M. Dovganiuk Electron and hole spectra in quantum wire with two quantum dots in the electric ﬁeld Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, Chernivtsi, Ukraine

64 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

31. K. Matyjasek and R.Z. Rogowski Dynamics of the domain structure in non-uniform ferroelectric crystals Institute of Physics, Szczecin University of Technology, Szczecin, Poland

32. M. Olszowya, Cz. Pawlaczykb, E. Markiewiczb, E. Nogas-Cwikiel´ c and J. Kulek b Dielectric behaviour and pyroelectricity in SBN70–PVC composites aUniversity of Zielona Góra, Institute of Physics, Zielona Góra, Poland bPolish Academy of Sciences, Institute of Molecular Physics, Poznań, Poland cUniversity of Silesia, Faculty of Computer and Materials Science, Sosnowiec, Poland

33. K. Ozgaa, A. Slezaka, K. Nounehb,c, I.V. Kitykd,b and S. Benetb Non-linear optical diagnostic of low temperature semimagnetic phase transitions aInstitute of Biology and Biophysics, Czestochowa University of Technology, Czestochowa, Poland bLaboratoire de Physique Appliquée et Automatique, Universitéde Perpignan, Perpignan, France cGroupe d’Etude des Semiconducteurs, CNRS-UMR 5650, Université Montpellier II, Montpellier, France dInstitute of Physics, Academy J. Dlugosz of Czestochowa, Czestochowa, Poland

34. R. Peleshchak, O. Dan’kiv and O. Odrekhivs’ka Dependence of energy of electronic transition in a quantum dot from symmetry of deformation ﬁeld Drohobych Ivan Franko state pedagogical university, Drohobych, Lviv region, Ukraine

35. R. Peleshchak, O. Kuzyk and V. Shtym Self-organizing of defect-deformation structures in crystals within the framework of electron-deformation model Drohobych Ivan Franko state pedagogical university, Drohobych, Lviv region, Ukraine

36. I. Polovynko and S. Rykhlyuk Raman studying of K2[Co(H2O)6](SO4)2 crystal Ivan Franko National University of Lviv, Faculty of Electronics, Lviv, Ukraine

37. I.P. Prits, S. Hasynets’, S. Motrya, O. Mykailo, V. Tovt and M. Potorii Tin hexathiohypodiphosphate and analogues: phase diagram, single crystal growth and properties Institute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine

65 4–7 September 2004, Lviv, Ukraine

38. I.P. Prits, I. Stoika, M. Gurzan, Yu.Yu. Gaza and M.M. Danko Tin hexathiohypodiphosphate single crystal growth Institute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine

39. I.V. Pylyuk Three-dimensional Ising-like system in an external ﬁeld: Microscopic calculation of the free energy in the higher non-Gaussian approximation Institute for Condensed Matter Physics, Lviv, Ukraine

40. I.M. Rizaka, V.S. Bilanychb and V.M. Rizakb Internal friction in the Sn2P2S6 ferroelectric aDnipropetrovsk National University, Dnipropetrovsk, Ukraine bUzhgorod National University, Uzhgorod, Ukraine

41. I.M. Rizaka, O.I. Chobalb and V.M. Rizakb Ab initio calculation of vibrational and electronic spectra of Sn2P2S6 ferroelectric crystals aDnipropetrovsk National University, Dnipropetrovsk, Ukraine bUzhgorod National University, Uzhgorod, Ukraine

42. L. Sadovskaya and K. Agarkov Properties of doped bismuth tellurite single crystals Dnipropetrovsk National University, Department of the solid state physics, Dnipropetrovsk, Ukraine

43. D.M. Berchaa,b and I.V. Slipukhinaa Effect of Ni substitutional impurities on the electronic properties of the ferroelectric SbSI crystal aInstitute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine bInstitute of Physics, University of Rzeszów, Rzeszów, Poland

44. A.G. Slivka, V.M. Kedyulich and A.I. Susla Pyroelectric properties of TGS crystals doped with metal atoms Uzhhorod National University, Optics Department, Uzhhorod, Ukraine

45. W. Smiga´ a, B. Garbarz-Glosa, G. Stopaa, J. Suchanicza, M. Dambekalneb, A. Stenbergb and Cz. Ku´sa The structural and dielectric properties of the Na0.96Li0.04NbO3 ceramic aInstitute of Physics, Pedagogical University, Krakow, Poland bInstitute of Solid State Physics, University of Latvia, Riga, Latvia

66 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

46. E.D. Soldatova and A. Galdina The conditions of the passage of phase equilibrium curve into the supercritical curve of lowered stability in the ferroelectric Lieb model Dnipropetrovs’k national university, Faculty of physics, Dnipropetrovs’k, Ukraine

47. S.I. Sorokov, R.R. Levitskii and A.S. Vdovych Dynamic susceptibility of proton-glass model with essential short-range interactions Institute for Condensed Matter Physics, Lviv, Ukraine

48. V.Yo. Stadnyka, M.M. Romanyukb and J. Stankowskac The optical properties of mechanically clutched TGS crystals with L-valine admixture aLviv Ivan Franko National University, Lviv, Ukraine bLviv Polytechnic National University, Lviv, Ukraine cPoznan Adam Mickevich University, Poznan, Poland

49. V.Yo. Stadnyk, M.O. Romanyuk, O.Z. Chyzh and V.F. Vachulovych The baric changes of the refractive properties of K2SO4 crystals Lviv Ivan Franko National University, Lviv, Ukraine

50. V.Yo. Stadnyk, M.O. Romanyuk and M.R. Tuzyak The inﬂuence of the mechanical pressure on the infrared spectra of (NH4)2SO4 crystals Lviv Ivan Franko National University, Lviv, Ukraine

51. O.V. Bovgyra, V.Yo. Stadnyk, A.V. Franiv, M.R. Tuzyak and O.Z. Chyzh The band energy structure of RbKSO4 crystals Lviv Ivan Franko National University, Lviv, Ukraine

52. I.V. Stasyuk and R. Stetsiv Equilibrium states and phase transitions in the crystals possessing chain structures with hydrogen bonds Institute for Condensed Matter Physics, Lviv, Ukraine

53. K. Strelets and T. Panchenko Photochromic eﬀect and induced photocondactivity in undoped and doped sillenite bismuth crystals Dnepropetrovsk National University, Faculty of physics, Dnepropetrovsk, Ukraine

67 4–7 September 2004, Lviv, Ukraine

54. I. Studenyaka and M. Kranjcecˇ b Temperature behaviour of order parameter in Cu6PSe5I(Br) superionic conductors aUzhhorod National University, Faculty of physics, Uzhhorod, Ukraine bUniversity of Zagreb, Faculty of Geotechnics, Varaˇzdin, Croatia

55. I. Studenyak, K. Rushchanskii and V. Stephanovich Phonon spectra of Cu6PS5Br superionic ferroelastic: experimental and theoretical studies Uzhhorod National University, Faculty of physics, Uzhhorod, Ukraine

56. J. Suchanicza, A. Kaniab, G. Stopaa and R. Bujakiewicz-Koronska´ a Inﬂuence of axial pressure on dielectric properties of AgNbO3 single crystals and ceramics aInstitute of Physics, Pedagogical Academy, Krakow, Poland bInstitute of Physics, University of Silesia, Katowice, Poland

57. S. Sveleba, O. Semotyuk, I. Katerynchuk and I. Kunyo Phase transitions caused by the incommensurate phase existence Ivan Franko National University of Lviv, Faculty of electronics, Lviv, Ukraine

58. M. Tkach and R. Fartushynskyi Electron-phonon interaction in two well spherical nanoheterosystem HgS/CdS/HgS/CdS Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, Chernivtsi, Ukraine

59. M.D. Volnianskii, M.P. Trubitsyn and Yahia A.H. Obaidat EPR and dielectric spectroscopy of the re-orienting Cr3+–Li+ pair centers in Li2Ge7O15 crystals Department of the solid state physics, Dnipropetrovsk National University, Dnipropetrovsk, Ukraine

60. T. Panchenko and A. Urchik Nonlinear electrophysics properties of the crystals Bi12SiO20 doped by Al and Ga ions Dniepropetrovsk National University, Dniepropetrovsk, Ukraine

61. Yu. Vasylkiv, Yu. Nastishin and R. Vlokh Conoscopic patterns for optically uniaxial gyrotropic crystals in the vicinity of isotropic point Institute of Physical Optics, Lviv, Ukraine

68 VIII Ukrainian-Polish and III East-European Meeting on Ferroelectrics

62. R. Vlokha, A. Saya, Ya. Buraka, O.V. Vlokha, I. Girnyka, Yu. Vasylkiva and Y. Uesub Domain structure in langbeinites. “Forbidden” domain walls aInstitute of Physical Optics, Lviv, Ukraine bWaseda University, Department of Physics, Tokyo, Japan

63. O. Voitsekhivska and A. Gryschyk Properties of interface phonon spectra in complicated cylindrical nanosystem Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, Chernivtsi, Ukraine

64. R. Yevych and Yu.M. Vysochanskii Temperature and pressure eﬀects on lattice dynamics of Sn2P2S6 monoclinic ferroelectrics Institute for Solid State Physics and Chemistry, Uzhgorod National University, Uzhgorod, Ukraine

65. Yu.I. Dublenych Phase transitions and phase separations in an S = 1/2 pseudospin-electron model and ferroelectricity in intercalated compounds Institute for Condensed Matter Physics, Lviv, Ukraine

66. R.R. Levitskiia, I.R. Zachekb and A.S. Dudaa Inﬂuence of σ1 − σ2 stress on transverse relaxation dynamics in the KD2PO4 type ferroelectrics aInstitute for Condensed Matter Physics, Lviv, Ukraine bLviv Polytechnical National University, Lviv, Ukraine

67. B. Mytsyk, A. Andrushchak, H. Haskevych and I. Solskii Inﬂuence of temperature on the piezo-optic eﬀect in LiNbO3:MgO crystals Lviv Center Institute Space Research, Lviv, Ukraine

68. R.R. Levitskiia, I.R. Zachekb and A.S. Vdovycha Thermodynamics and relaxational dynamics of the KH2PO4 type ferroelectric compounds: a uniﬁed model aInstitute for Condensed Matter Physics, Lviv, Ukraine bLviv Polytechnical National University, Lviv, Ukraine

69 4–7 September 2004, Lviv, Ukraine

69. R. Poprawski, A. Cizman˙ and A. Sieradzki Ferroelectric phase transition in (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 crystals Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland 70. A. Cizman˙ a, R. Poprawskia, D. Wlosewicz b and A. Sieradzkia Phase transitions in (TEA)2MnCl4 crystals aInstitute of Physics, Wroclaw University of Technology, Wroclaw, Poland bInstitute of Low Temperature and Structure Research, Wrocl aw, Poland 71. E. Rysiakiewicz-Pasek, R. Poprawski, A. Sieradzki and J. Polanska Dielectric properties and phase transitions of KNO3 embedded into porous glasses Institute of Physics, Wroclaw University of Technology, Wroclaw, Poland 72. O. Czupinski´ a, M. Wojta´sa, A. Pietraszkob and R. Jakubasa Phase situation in cyanopiridinium perchlorate crystals [CNC5H4NH][ClO4] aFaculty of Chemistry, University of Wroclaw, Wroclaw, Poland bInstitute of Low Temperature and Structure Research, Wrocl aw, Poland 73. O.Yu. Shulichenko Electromechanical properties of crystals in system Li2Ge4O9–LiNaGe4O9 Dnipropetrovsk National University, Dnipropetrovsk, Ukraine

70 Tuesday, September 5 P1

Band structure and optical spectra of ferroelectric triglycine sulfate

B. Andriyevskya, W. Ciepluch-Trojaneka, A. Patryna, N. Esserb, C. Cobetb and M.M. Romanyukc aKoszalin University of Technology, Faculty of electronics and computer sciences, 2 Sniadeckich Str., 75–453 Koszalin, Poland, E–mail: [email protected] bISAS – Institute for Analytical Sciences Department Berlin, Albert-Einstein-Street 9, D–12489 Berlin, Germany cIvan Franko National University of Lviv, Faculty of physics, 8 Kyrylo i Mefodij Str., 79005 Lviv, Ukraine

First-principal calculations of the band structure, density of electronic states, and dielectric functions of the triglycine sulfate crystal (TGS) in the ferroelectric phase together with the corresponding experimental ellipsometric spectra in the range of 4. . . 10 eV have been presented for the first time. Calculations have been performed in the frame of density functional theory using the CASTEP code. Experimental data have been obtained using the radiation of BESSY synchrotron source. The dispersion of energy bands E(k) of TGS crystals is mainly flat with great ∗ ∗ effective masses m ≥ 10me, however smaller magnitudes m ≈ 0.5me also take place. Energy band gap of the crystal is confirmed to be indirect and corresponds to the optical transition between Γ and D points of the Brillouin zone (BZ). An upper part of the valence band (−3.0 . . . 0.5 eV) is mainly (0.95) of 2pO-origin. Electron states of the lower part of the conduction band (4.0 . . . 6.0 eV) are also mainly of the p-type (0.80) originated from three glycine groups having the antibonding character. Theoretical dielectric functions 00(ω) of TGS crystal agrees satisfactorily with corresponding experimental dependencies obtained in the spectral range of 4 . . . 10 eV. Strong spectral band of 00(ω) with maximum at ω = 7.3 eV corresponds to the direct optical transitions in the Γ-, Y -, B-, and E-points of BZ between the upper valence band at −1.07 . . .−0.25 eV and the conducting band at 5.4 . . . 6.5 eV. Long-wavelength fundamental optical absorption of TGS crystal (ω ≈ 5.0 eV) can be assign to the indirect transitions of localized type realizing between the p-states of oxygen atoms of separate glycine groups.

71 P2 Tuesday, September 5

Inﬂuence of hydrostatic pressure on structural and electronic parameters of TGS crystals (ﬁrst-principal calculations)

B. Andriyevsky, W. Ciepluch-Trojanek and A. Patryn Koszalin University of Technology, Faculty of electronics and computer sciences, 2 Sniadeckich Str., 75–453 Koszalin, Poland, E–mail: [email protected]

The triglycine sulfate crystal (TGS) is a low-packed ferroelectric material with the relatively small density (ρ = 1.69 g/cm3). It is interesting to study the influence of hydrostatic pressure on the structural and electronic parameters of this material, because of the presence of different types of chemical bonds between atoms in the crystal. First principal calculations of the influence of hydrostatic pressure on the structural and electronic parameters of TGS crystals have been carried out for the first time. The calculations have been done in the frame of density functional theory using the Cambridge Serial Total Energy Package code (CASTEP). Calculations of the optimized atomic structures and corresponding electronic parameters of the crystal have been done for certain magnitudes of hydrostatic pressure in the range of −10 . . . 150 GPa. Hydrostatic pressure was applying to the crystal being in the space groups of symmetry 4 (ferroelectric phase), 11 (paraelectric phase), and 1. The volume dependence of total electron energy E(V ) of the crystal unit cell satisfies the third-order Birch-Murnaghan isothermal equation of state. Using this equation, the bulk modulus K and its derivative K0 in the ferroelectric phase were found to be equal to K = 45.3 ± 4.8 GPa and K0 = 3.07 ± 2.8 for the pressure range of −2 . . . 5 GPa. The analogous values for the pressure range of −10 . . . 150 GPa are equal to K = 43.4 ± 2.8 GPa and K0 = 3.14 ± 0.11. The relative pressure changes of the unit cell parameters were found to be linear in the range of −5 . . . 5 GPa. Substantial nonlinearity of these dependencies becomes visible already in the range of 0 . . . 30 GPa. Pressure dependencies of the enthalpy, H = E + P V , have revealed that enthalpy of the crystal in the paraelectric phase becomes smaller than that for the ferroelectric phase for the pressure P > 7 GPa. This permits to suggest a pressure induced phase transition in TGS crystal from the ferroelectric to the paraelectric phase.

72 Tuesday, September 5 P3

Theoretical investigation of the thermodynamic and dynamic properties of the crystals with asymmetric double-well potential within the framework of the Mitsui model taking into account tunnelling eﬀects and piezoelectric interaction

R.R. Levitskiia, I.R. Zachekb, A.Ya. Andrusyka and I.V. Kutnyc aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bNational University “Lviv Polytechnic”, Faculty of physics, 12 Bandera Str., 79013 Lviv, Ukraine cLviv Commercial Academy, 10 Tuhan-Baranovskii Str., 79005 Lviv, Ukraine

We investigate the phase transitions and physical properties of the Rochelle salt (double sodium-potassium tartrate NaKC4H4O6 ·4H2O), RbHSO4 and NH4HSO4 crystals. As a model describing these crystals we used the Mitsui model taking into account tunnelling effects. For Rochelle salt, in particular, we used the Mitsui model adjusted by considering the piezoelectric coupling with shear strain ε4 [1]. All physical characteristics were derived within the molecular field approximation. Theory model parameters were obtained for every crystal, and on their basis the thermodynamic characteristics were calculated and compared to the experimental ones. Also we investigate high frequency relaxation dynamics of the Rochelle salt and RbHSO4 using the Bloch equations method. We derived relaxation times and real and imaginary part of the dielectric susceptibility and compared them all to the experiments and to the results of the work [1] derived within the model without taking into account tunnelling effects and within the Glauber equations for the dynamic properties. The both free and clamped crystal regimes were investigated for the dielectric permittivity of the Rochelle salt. The problem of bounds for isolated, isothermal and adiabatic susceptibilities between each other and their correspondence to the experiment were discussed in details.

1. R.R. Levitskii, I.R. Zachek, T.M. Verkholyak and A.P. Moina // Physical Review B 67, 174112 (2003).

73 P4 Tuesday, September 5

Investigation of the hydrostatic pressure inﬂuence on the phase transitions and physical properties of the Rochelle salt and RbHSO4 crystals R.R. Levitskiia, A.P. Moinaa, I.R. Zachekb, A.Ya. Andrusyka, A.G. Slivkac and V.M. Kedyulichc aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bLviv Polytechnical National University, 12 Bandera Str., 79013 Lviv, Ukraine, cUzhgorod National University, 54 Voloshin Str., 88000 Uzhgorod, Ukraine

We study the influence of hydrostatic pressure on the phase transition of Rochelle salt and RbHSO4 crystals within the Mitsui model. For Rochelle salt, in particular, we used the two-sublattice Mitsui model modified by considering the piezoelectric coupling with shear strain ε4. All thermodynamic characteristics were derived within the molecular field approximation. A phenomenological model, which consists of assumption of the linear dependence of the model parameters upon pressure, is proposed. Under this assumption such values of the model parameters are found, which provide a good agreement with experimental datal for the pressure dependency of the phase transition temperatures for both Rochelle salt and RbHSO4 crystals. The same phenomena are also considered within a more consistent model, where the parameters of the modified Mitsui model are assumed linear functions of the diagonal components of the lattice strain tensor. Theoretically calculated static dielectric permittivity of mechanically free Rochelle salt crystal is compared to the experimental one; a satisfactory agreement between them is revealed for the vicinity of the upper Curie temperature. The static permittivity of a deformed RbHSO4 crystal also agrees well with experimental data. Other thermodynamic characteristics (polarization, specific heat) are calculated for both crystals under investigation at different hydrostatic pressures within the proposed model.

74 Tuesday, September 5 P5

Elementary energy bands concept in IV-VI crystals with phase transitions

D.M. Berchaa,b, L.Yu. Kharkhalisa, I.V. Slipukhinaa and M. Sznajderb aInstitute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn St., 88000 Uzhgorod, Ukraine, E–mail: [email protected] bInstitute of Physics, University of Rzesz´ow, Rejtana 16a, 35–310 Rzesz´ow, Poland, E–mail: [email protected]

In this paper we consider the possibility to extend the elementary energy bands concept onto the systems, in which phase transformations are induced by the deviations from stoichiometry. Some narrow-gap IV-VI-type semiconducting ferroelectrics are considered as an example. As is known, several phase transitions are observed in these crystals. It is shown that a possibility to explain the band structure transformations accompanying the phase transitions in such type compounds with non-stoichiometric composition exists. This possibility is based solely on the information about the symmetry of elementary energy bands in the band spectrum of a given phase and the local symmetry of the related specific Wyckoff positions. In particular, possible reasons of fourfold enlargement of the crystal’s unit cell during phase transition from the cubic 5 16 modification (Oh symmetry) to the orthorhombic one (D2h symmetry) are discussed. It turns out that this phase transition is accompanied by an increase of the degrees of freedom of the specific Wyckoff position as a result of symmetry lowering. Such transformations of band spectrum in IV-VI-type crystals with super-stoichiometric atoms are caused by the electron density redistribution within the unit cell, and this in turn essentially influences the redistribution of electrons between occupied and unoccupied states in the k-space, which is probably caused by electron-phonon coupling. We con- clude that the existence of close interrelation between the distribution of electrons in the direct and reciprocal spaces allows one to make predictions about the possibility of structural transformations, using the information about the evolution of electronic energy spectrum in the reciprocal space.

75 P6 Tuesday, September 5

Optical and photoelectric parameters of doped Sn2P2S6 ferroelectric crystals

K.V. Bodnar, A.A. Grabar, I.V. Kedyk, Yu.Yu. Gaza, M.M. Danko, L.S. Gaza and Yu.M. Vysochanskii Institute for Solid State Physics and Chemistry of Uzhgorod National University, Pidhirna 46, 88000 Uzhgorod, Ukraine, E–mail: [email protected]

The Sn2P2S6 crystals are promising photorefractive materials for red and near infrared spectral range with high amplitude parameters and fast enough response time. Enhancement of these properties can be achieved by variation of the growth technology, but also by goaled doping. In the communication the experimental data on the optical and photoelectric spectra, as well as the photorefractive parameters of such crystals, enhanced by goaled doping by Te, Bi, and Sb are presented. All these crystals were grown by vapor-transport technique using stoichiometric Sn2P2S6 composition with an additional amount of the dopants. Our measurements of the optical transmission show that the absorption spectra of the doped crystals contain an additional band near the fundamental absorption edge, and the optical absorption near this band increases with concentration of dopants. However, the shapes of the absorption bands in the doped crystals obtained at substitution of chalcogen atoms (Sn2P2S6:Te) and by fifth group elements (Sn2P2S6:Sb, Bi), are different. This difference manifests itself also in the photoconductivity spectra, measured at DC in the 500– 1000 nm spectral range. In all cases the doping leads to increasing the photosensitivity near these impurity bands, enhancing the photorefractive response. The basic photorefractive parameters were measured using conventional holographic technique using He-Ne laser (633 nm), and the two-wave mixing gain Γ and the response time τ were measured. It was found that the doped crystals exhibit larger max −1 −1 gain coefficients (up to 15 cm in Sn2P2S6:Te, and 20 cm in Sn2P2S6:Sb), that is much larger as compared to Γ = 5 . . . 7 cm−1, typically observed in nominally pure Sn2P2S6. Basing on the results of the dielectric and photorefractive measurements, the microscopic parameters responsible for photorefractive effect in these doped crystals have been estimated. Potential applications of the Sn2P2S6:Te(Sb,Bi) crystals are also discussed.

76 Tuesday, September 5 P7

Dielectric and pyroelectric properties of the Ba0,3Na0,7Ti0,3Nb0,7O3 ceramics obtained by sol-gel method

K. Cwikiel´ a and E. Nogas-Cwikiel´ b aUniversity of Silesia, A. Che lkowski Institute of Physics, 4 Uniwersytecka St., 40–007 Katowice, Poland, E–mail: [email protected] bUniversity of Silesia, Faculty of Computer Science and Materials Science, 2 Snie˙zna St., 41–200 Sosnowiec, Poland

Solid solution of barium titanate BaTiO3 and sodium niobate NaNbO3 – Ba1−xNaxTi1−xNbxO3 (BNTN) is a new lead-free material. BNTN ceramics obtained by conventional ceramic method present the classical ferroelectric character when 0

1. Khemakhem H., Simon A., Von Der Mühll R., Ravez J., Journal of Physics: Con- densed Matter 12 (2000) 5951–5959. 2. Abdelkefi H., Khemakhem H., Velu G., Carru J., Von der Mühll R., Solid State Sciences 6 (2004) 1347–1351.

77 P8 Tuesday, September 5

Dielectric properties of [(CH3)2NH2]3CuCl5 in external electric ﬁeld

S. Dacko, Yu. Eliyashevskyy and Z. Czapla Wroclaw University, Institute of Experimental Physics, Max Born Sq. 9, 50–204 Wroclaw, Poland, E–mail: [email protected]

The crystal of [(CH3)2NH2]3CuCl5 exhibits a sequence of phase transitions which is presented according to the scheme: 253 K 278K T, K P222 Pcca or Pna2 Pna2 1 PE FE T Tc2 c1 The phase existing in the range of 278–253 K is a ferroelectric one with practically constant value of spontaneous polarization equal to 3.5 · 10−2 Cm−2. In this paper the detailed studies of dielectric properties of [(CH3)2NH2]3CuCl5 single crystal were performed along the ferroelectric crystallographic a-axis in the vicinity of phase transition from para- to ferroelectric phase under influence of electric field intensity. In the experiment we observed insignificant shift of the ferroelectric phase transition at Tc1 to higher temperatures and the diffused maxima of permittivity. Significant shift of permittivity maximum was found with increase of electric field intensity. Observed results one can interpret as coexistence of para- and ferroelectric phases. Additionally, the time dependences of electric permittivity and depolarization current after applying of electric at different temperatures above Tc1 were studied. The strong changes of permittivity were observed in these measurement. These results showed the relation between the changes of permittivity and induced polarization and allowed to find internal electric Eb existing in studied samples.

78 Tuesday, September 5 P9

Protonation and conductivity of Na0.5Bi0.5TiO3 ceramics at high temperature

V.M. Duda and T.V. Kruzina Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, Dnipropetrovsk 49050, Ukraine, E–mail: duda@ﬀ.dsu.dp.ua

Hydrogen may be incorporated as defects in oxides [1]. Presented in significant concentration it may affect the defect-dependent properties of these materials. In the present communication we report the results of the protonation influence on the change transport processes of relaxor ferroelectric ceramic Na0.5Bi0.5TiO3 (NBT) in the temperature range 450◦C–850◦C. Polycrystalline samples of NBT were obtained by usual ceramic technology. The ac-impedance spectra in the frequency range from 5 Hz to 13 MHz was measured by HP-4192 ALF impedance analyzer. Measurements were performed upon cooling after samples were annealed in dry or moist N2 gas atmospheres. The data were plotted in the Z00 − Z0 complex impedance plane. Calculated from the semicircle high-frequency portion of spectra at different temperatures dc-conductivity values show Arrhenius behavior ln σ(0) = (1/T ). The decreased σ(0) obtained in moist N2 atmosphere as compared to measurements in dry N2 environment may indicate that protons are im- planted in NBT crystalline lattice. But the water vapor partial pressure PH2O does not influence on the electron (hole) conduction. It seems that in N2 atmosphere the removal of oxygen atoms leads to the ion (oxygen) conductivity due to the vacancy mechanism. In moist N2 environment as the result of the following reaction

¨ × ˙ H2O(gas) + V0 +O0 ↔ 2OH0 the decrease of the vacancy concentration but incorporation of protons in the form of hydroxyl ions OH is observed and “vehicular” mechanism of the proton transport is possible.

1. T. Norsy, Adv. Ceram. 23 (1987) 107.

79 P 10 Tuesday, September 5

Nonstoichiometry and conductivity of Pb5Ge3O11 single crystals

V.M. Duda, A.S. Ermakov, V.G. Linnik and A.S. Belous Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, 49050 Dnipropetrovsk, Ukraine, E–mail: duda@ﬀ.dsu.dp.ua

The influence of nonstoichiometry on the electrical conduction of Pb5Ge3O11 single crystals in c-direction has been studied in the temperature range 180–300◦C. The crystals were grown by Czochralski method. The ratio of initial oxides PbO and GeO2 for synthesis corresponded to the nonstoichiometric chemical formula Pb5+xGe3O11+x (x = −0.05; 0.00; +0.05). Measurements were carried out by the bridge method in the frequency range 50 Hz – 18 kHz. Experimental data were plotted in G00 − G0 complex admittance plane. Hodographs had the form of straight lines. This means that in the given frequency range the sample is equivalent to a parallel RC-circuit. DC-conduction value G(0) is given by intersection of hodographs with real axis G0. DC-conductivity G(0) have been calculated and the temperature dependances for crystals of different composition have been plotted. These functions are mapped as straight lines in the Ar- rhenius plot (ln G(0) = f(1/T )), indicating that the charge transfer in lead germanate crystals is thermally activated. In investigated temperature range the conductivity values increase with the x decrease. It seems that there is no way to completely prevent loss of the volatile PbO during high-temperature synthesis and growth of the single crystals. So the ratio of initial oxides PbO and GeO2 in the end product (crystal) differs in Pb5Ge3O11 from the stoichiometric ratio (5:3). It has been shown [1] that in this case actually the formula of nonstoichiometric lead germanate should be written as Pb5−xGe3O11−x+δ. It means that the concentration of lead vacancies exceeds the concentration of oxygen vacancies. To maintain the electrical neutrality of the entire crystal the valence of lead cations should be changed Pb2+ −→ Pb4+(Pb3+) that is the reason of the electronic p-type conduction observed experimentally. It is supposed that with the x increase concentration of lead vacancies decreases that may be the reason of the reduction of p-type conductivity in Pb5Ge3O11 crystals.

1. V.M. Duda, A.I. Baranov, A.S. Ermakov, R.C.T. Slade. Physics of Solid State, 2006, vol. 48, No. 1, pp. 63–67.

80 Tuesday, September 5 P 11

Antiferroelectric thin ﬁlms phase diagrams

E.A. Eliseeva, M.D. Glinchuka and A.N. Morozovskab aInstitute for Problems of Materials Science, NAS of Ukraine, Krjijanovskogo 3, 03142 Kiev, Ukraine, E–mail: [email protected] bV. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 41, pr. Nauki, 03028 Kiev, Ukraine, E–mail: [email protected]

In the paper we consider size effects on phase transitions and polar properties of the thin antiferroelectric films. We modified phenomenological approach proposed by Kittel taking into account the correlation energy and depolarization field for the thin films. The free energy with renormalized coefficients depending on the film thickness has been derived. The approximate analytical expression for the paraelectric-antiferroelectric- ferroelectric transition temperatures dependence on film thickness, polarization gradient coefficient and extrapolation lengths was obtained. The critical value of the electric field that induces antiferroelectric-ferroelectric phase transition was calculated. Allowing for the renormalized coefficients thickness dependence this value could be essentially smaller than the electric field necessary for the antiferroelectric-ferroelectric phase transition in the bulk material. The field could be built-in, in particular caused by a film-substrate lattice mismatch effect and it can induce the transition from antiferroelectric to ferroelectric without application of the external field. We have shown how the anti-ferroelectric “double” hysteresis loop transforms into the ferroelectric “single” one under the film thickness decrease. Proposed theoretical consideration explains the experimental results obtained earlier in antiferroelectric PbZrO3 thin films.

81 P 12 Tuesday, September 5

Inﬂuence of the hydrostatic pressure on phase transitions of [(CH3)2NH2]3CuCl5 crystals Yu. Eliyashevskyya, A. Sieradzkib, R. Poprawskib and Z. Czaplaa aWroclaw University, Institute of Experimental Physics, Max Born Sq. 9, 50–204 Wroclaw, Poland, E–mail: [email protected] bWroclaw University of Technology, Institute of Physics, Wybrze˙ze Wyspia´nskiego 27, 50–370 Wroclaw, Poland

At atmospheric pressure tris-dimethylammonium pentachlorocuprate [(CH3)2NH2]3CuCl5 exhibit first-order ferroelectric phase transitions at about Tc1 = 279 K and another first-order phase transition at Tc2 = 253 K. The results of investigations of the influence of the hydrostatic pressure on dielectric properties and phase transitions are presented. The disappearance of the ferroelectric phase at Ts = 265 K and ps = 45 MPa was found. The negative and nonlinear shift of phase transition at pressures higher that ps was observed. The phase diagram obtained on the basis of isotherm and isobars families is presented on Fig. 1.

280

270 , K

c1,2 T 260

250

0 50 100 150 200 250 p, MPa

Figure 1: The temperature-pressure phase diagram of [(CH3)2NH2]3CuCl5 crystals.

82 Tuesday, September 5 P 13

Synthesis, microstructure and dielectric properties of (1 − x)PSN–xPLuN

B. Garbarz-Glosa, W. Smiga´ a, J. Suchanicza, D. Sitkoa, M. Dambekalneb, A. Sternbergb and D. Sko lyszewskia aInstitute of Physics, Pedagogical Academy of Krakow, Poland bInstitute of Solid State Physics, University of Latvia, Latvia

Perowskite relaxor ferroelectrics reprezent the widest application area of ferroelectric materials, for their electromechanical, optical and dielectric properties. They exhibit a dispersive dielectric response near the ferroelectric phase transition, and this relaxor behavior is thought to be related to local disorder. Relaxor ferroelectrics, or 0 00 relaxors, are complex lead based perovskites with general formula Pb(B B )O3, where B0 is a low-valence cation and B00 is high-valence cation. Ceramic lead niobates and their solid solutions PSN–PLuN were synthesized by solid state reactions from oxides. Ceramic samples have been obtained by both conventional and hot pressing techniques. The sequence of phases formed at PSN-PLuN synthesis has been studied by X-ray analysis. X-ray diﬀraction measurements were performed by XRD-7 diﬀractometer with CuKα radiation. Ceramic microstructure was studied by SEM with energy dispersive detector for X-rays (EDX). Temperature measurements of electric permittivity and electric hysteresis loops of the 0.9PSN–0.1PluN and 0.75PSN–0.25PLuN ceramics have been carried out. The values of the remenent polarization have been determined.

83 P 14 Tuesday, September 5

Raman scattering in macro- and mesoscopic Sn2P2S6 ferroelectrics

A.V. Gomonnai Institute of Electron Physics, Ukr. Nat. Acad. Sci., Universytetska Str. 21, 88017 Uzhhorod, Ukraine, E–mail: [email protected]

Ferroelectrics of Sn2P2S6 family have become an object of extensive experimental and theoretical interest in view of phase transitions and polycritical phenomena which are observed at the variation of temperature, pressure and mixed crystal composition. In the recent years a considerable attention is attracted to the studies of semiconductor microcrystals whose specific properties, resulting from the spatial confinement of charge-carriers, have determined a wide variety of promising application possibilities. Raman scattering spectroscopy is a powerful tool enabling, complementary to X-ray diffraction, estimation of microcrystal size, composition and other factors, affecting the lattice dynamics. Nanometer-scale Sn2P2S6 crystalline powders were obtained by milling, the average nanocrystal size ranging down to 9 nm, as estimated from X-ray diffraction and TEM studies [1]. Raman scattering studies of the nanocrystalline powders have shown the general resemblance of the spectra with those of similar bulk crystals, however, with some additional features, specific for the Raman spectra of the finest powder fractions. Namely, the observed slight downward shift and considerable broadening of Raman peaks with the average grain size decrease, is explained by the increasing role of the surface phonons due to the high surface-to-volume ratio in nanocrystals. The contribution of the confinement-related selection rules relaxation into the observed effect is discussed. The measurements carried out for Sn2P2(S1−xSex)6 solid solutions, have shown the 4− possibility of a variety of (P2S6−mSem) anions with partly (m = 1, 2,..., 5) substituted chalcogen atom to be formed. The bands, corresponding to such groups, were clearly observed in the Raman spectra, particularly for the P–P bond vibration band, 4− as distinct separate peaks with frequencies, intermediate between those for (P2S6) 4− −1 and (P2Se6) anions. An additional band at 406 cm , revealed only for the finest 4− powder fractions, is related to the partial substitution of sulphur in (P2S6) anions by oxygen at the nanocrystal surface.

1. A.V. Gomonnai, Yu.M. Azhniuk, Yu.M. Vysochanskii, A.A. Kikineshi, M. Kis-Varga, L. Daroczy, I.P. Prits, I.M. Voynarovych, J. Phys.: Condens. Matter. 15, 6381 (2003).

84 Tuesday, September 5 P 15

Dielectric investigation of 2-aminopyridyne phosphate crystal

A. Hek, S. Dacko and Z. Czapla Wroclaw University, Institute of Experimental Physics, Max Born Sq. 9, 50–204 Wroclaw, Poland, E–mail: [email protected]

The 2-aminopirydyne phosphate (NC4H4NH2 · H3PO4) is a new hydrogen-bonded crystal exhibiting the ferroelectric phase transition at 103.5 K [1]. At room temperature the crystal belongs to monoclinic space group C2/c with eight molecular units per unit cell [1]. The spontaneous polarization is placed in ac plane, and has major component along the crystallographic a-axis. The value of spontaneous polarization is equal to 8.7 · 10−3 C m−2 at 80 K. The molecular mechanism of phase transition seemed to be related to ordering of proton in hydrogen bonds linking PO4 tetrahedra into infinite chains along the crystallographic a-axis [1]. The phase transition is second-order [2]. The complementary measurements of the dielectric dispersion in ferroelectric phase of 2-APP crystal at frequency range 2 kHz–1 MHz has been carried out. Data points were stored for different amplitude of the measured field. Dielectric spectra have been analyzed using the Cole-Cole formula:

∗ ε − ε∞ 1 = 1−β . (1) εS − ε∞ 1+(iωτ0) At this range of frequency we found one relaxation process. The temperature dependence of the relaxation time of this process has been calculated. According to the Arrhenius theory the activation energy of this process was obtained.

1. Z. Czapla, S. Dacko, and A. Wa´skowska, J. Phys.: Condens. Matter, 15, 3793 (2003). 2. A. Hek, S. Dacko, Z. Czapla, and R. Cach, Phys. Stat. Sol. (b), 240, 649 (2003).

85 P 16 Tuesday, September 5

Electron energy spectrum in core-shell elliptic quantum wire

V. Holovatsky and V. Gutsul Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, 2 Kotsubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

Nanostructures, such as nanotubes, nanowires, and quantum dots offer possibilities for creation of new logical circuits, ultra small light emitters and nanoscale photodetec- tors. Their potential abilities can be greatly enhanced by introducing heterostructures within quantum dots and nanowires. Modern technologies permit to grow the multishell heterostructure nanowires. In order to utilize such nanoconstructions in modern optical devices it is necessary to investigate the quasiparticles energy dependencies on the shape and geometrical sizes of multishell nanowires component parts. In this paper the electron energy spectrum in complicated elliptic quantum wire (CEQW) consisting of semiconductor elliptic wire covered by semiconductor elliptic shell embedded into dielectrical matrix is investigated within the effective mass approximation. In elliptic coordinates it is obtain the solution of Schrodinger equation at the finite height of the potential barrier at the interface of core-shell and infinite electron potential energy in the matrix. The focuses of the inner and outer elliptic interfaces coincide, therefore ellipticity of inner ellipse is bigger than outer one. It is shown that the ellipticity of quantum wire breaks the degeneration of quasiparticle energy spectrum. The energy dependencies of odd and even electron states on the ratio between semiaxes have a non- monotonous character. In the limit case of the degeneracy of elliptic quantum wires and elliptic nanotubes into cylindrical ones the quasiparticle energy spectrum coincides with the corresponding quasiparticle spectrum in cylindrical nanosystems. The anti crossing effects are observed at the dependencies of electron energy spectrum on the transversal sizes of the CEQW.

86 Tuesday, September 5 P 17

The temperature – time eﬀects in the incommensurate phase of [N(CH3)4]2CuCl4 and [N(CH3)4]2ZnCl4 crystals I. Katerynchuka, S. Svelebaa, O. Semotyuka, I. Kunyoa and Yu. Pankivskyib aDepartment of Nonlinear Optics, Lviv National Ivan Franko University, Tarnavskogo Str. 107, 79017 Lviv, Ukraine, E–mail: [email protected] bDepartment of Ecology, Ukrainian National University of Forestry, O. Kobylyanskoyi Str. 1, 79005 Lviv, Ukraine

The time and thermal dependencies of the optical birefringence increment (δ(∆n)) and the residual intensity (Ir) for [N(CH3)4]2CuCl4 and [N(CH3)4]2ZnCl4 crystals have been measured in the ranges of incommensurate phase existence. The cascades of transitions between metastable states to the equilibrium states on the time dependencies of δ(∆n) and Ir were obtained during temperature stabilization in the incommensurate phase (Tst = 293 K; 294 K; 294.5 K) of [N(CH3)4]2CuCl4 crystal. The amplitude of observed anomalies increases with approaching to Tc. It corresponds to the transition of the incommensurate structure to the soliton mode. The same character one can observe on the dependency of residual intensity. The relaxation character of this crystal was explained using the force-velocity dependence model. The time dependencies of residual intencity of [N(CH3)4]2ZnCl4 crystal were obtained at T = 293 K. The dynamics of the sample thermal mode was measured simultaneously. Due to the obtained results the transitions between metastable states are accompanied by discharges of heat. This effect is caused by calorification of excessive heat of modulation structure in the process of transition to the new metastable state. The potential energy of modulated structure pining on the defects transforms in the kinetic energy of modulated structure motion to the new metastable state. In support of last one conclusion the investigations of conjugate electric field Ea influence on modulated structure were performed. This kind of field changes the position of the minimum point on the thermodynamic potential curve. The Ea application and switching off are followed by changes of the temperature regime of the crystal. It is explained by the dynamics of modulated structure.

87 P 18 Tuesday, September 5

Eﬀect of external pressure and electric ﬁeld on the dielectric properties of Rochelle salt

V.M. Kedyulich, H.M. Guyvan and A.G. Slivka Uzhhorod National University, Optics Department, 54 Voloshyn Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected]

Temperature dependences of dielectric permeability of Rochelle salt crystals along the polar direction under uniaxial pressure of various symmetry σi(i = 1,..., 4) and external longitudinal and transverse electric field of different strength are studied. Ap- plication of uniaxial stresses is shown to result in a smearing of ε(T ) dependences, decrease of the maximal values of dielectric permeability in the vicinity of phase transition temperatures and variation of the temperatures Tm1 and Tm2, corresponding to these maxima. The temperature dependences of the Rochelle salt dielectric permeability under uniaxial stress are similar to the dependences obtained under longitudinal electric field. Uniaxial stress-induced shift ∆Tm results from the variation of the phase transition temperature ∆T0(σi) and shift of the temperature of the dielectric permeability maximum ∆Tm(E) due to piezoeffect. From the experimental studies of ∆Tm(σ) and ∆Tm(E) we have calculated the ∆T0(σi) dependences for both phase transitions. This has enabled the (σi, T ) diagrams for the Rochelle salt crystals to be built. At the application of normal σ1 and shear σ4 stress to the crystal the upper phase transition temperature T2 increases while that of the lower one T1 decreases. At normal stresses σ2, σ3 an opposite effect is observed: the increase of σ2 and σ3 values results in the increase of T1 and the decrease of T2. The pressure coefficients for the temperatures of both phase transitions are determined. Application of transverse electric field E⊥ results in a longitudinal field appearing in the sample due to charge redistribution over the systems of contacts, this determining the different behaviour of the ∆Tm(E⊥) dependences for different samples. Having excluded the effect of this field at the analysis of the experimental results, we have shown that the temperature of the upper phase transition for the Rochelle salt crystals decreases with the transverse electric field at a rate ∂T0/∂E⊥ = −0.5 K·cm/kV.

88 Tuesday, September 5 P 19

Birefringence of the linearly polarized light in the magnetoelectric single crystal LiNiPO4 Yu. Kharchenko Institute for Low Temperature Physics and Engineering, NASU, 47 Lenin ave., 61103 Kharkiv, Ukraine, E–mail: [email protected]

Among sets of the magnetoelectrics there is a well-known family of the orthorhombic antiferromagnetic crystals of LiMPO4 where M is an ion of a 3d-transition element. Though these crystals have been firstly synthesized and found to be magnetoelectric as early as in 1969 recently discovered properties of LiCoPO4 and LiNiPO4 that are unconventionally and seem unusual at present became the reason of a revival of interest in them. Subject of our studies was LiNiPO4. Its yet not explained properties are a unconventional hysteretic magnetoelectric properties and a recently discovered an ultra weak ferromagnetism. Besides the intermediate incommensurable magnetic structure was revealed recently near the Neel temperature. For more information about a magnetic ordering in this crystal the linear birefringence was investigated depending on changes of temperature and intensity of a magnetic field. Results of the carried out experiments are next. Jump- and kink-like peculiarities on the temperature dependence of the linear birefringence were observed at the TN1 and TN2 = TN1 + 1 K temperatures. Besides, the temperature hysteresis with width near 6 K was observed in the vicinity of the magnetic ordering temperature. These features agree with presence of a incommensurable magnetic structure in the temperature interval TN1 ÷ TN2. In addition, we observed the magnetic birefringence of a linearly polarized light that was directly proportional to magnetic field strength up to 15 kOe. In higher magnetic fields, after discontinuous jump the dependence acquire parabolic character. The attempt is made to connect observed properties with supposed peculiarities of the magnetic structure of the LiNiPO4 and with its behavior in a magnetic field.

89 P 20 Tuesday, September 5

High-ﬁeld magnetization of magnetoelectric antiferromagnet LiCoPO4 V. Khrustalyov, V. Savitsky and M. Kharchenko Institute for Low Temperature Physics and Engineering, NASU, 47 Lenin ave., 61103 Kharkiv, Ukraine, E–mail: [email protected]

Subject of our studies is single crystal of noncentrosymmetrical antiferromagnet LiCoPO4. This compound belongs to the olivine family of orthorhombic antiferromag- 2+ 2+ 2+ 2+ nets with the general formula LiMPO4 (M = Co , Ni , Mn , Fe ). The results of low-temperature measurements of differential magnetic susceptibility in a pulse magnetic field up to 300 kOe are presented. The measurements are carried out in longitudinal geometry (H k b k antiferromagnetic axis) in temperature interval 1.6–20.4 K. Under influence of magnetic field several magnetization jumps occur. So at liquid helium temperatures (1.6–4.2 K) two peaks on the curve dM/dH were observed at field strengths near to H1 = 120 kOe, H2 = 226 kOe, and the step-like feature at field H3 = 275 kOe have been discovered. The shapes of detected peaks are different and the first one has the structure, which changes under different conditions of experiments, such as temperature or a velocity of field changing. Magnetization is not finishing when magnetic field reaches value H2 (as it was assumed earlier. Transition to the saturated paramagnetic state occurs at the field strength H3 = 275 kOe (4.2 K). Magnetization is increased monotonously with rising of magnetic field from H2 to H3. The observed peculiarities mean that the magnetic-field-induced structures are complicated ones, and their magnetic cells are essential different. On experimental data the magnetic (H − T ) phase diagram has been constructed and the magnetic moment in saturation for LiCoPO4 was obtained (450 G or 3.4 µb/ion).

90 Tuesday, September 5 P 21

Pyroelectric study of Na1−xLixNbO3 ceramic K. Konieczny, W. Smiga,´ B. Garbarz-Glos, G. Stopa and Cz. Ku´s Institute of Physics, Pedagogical University, Podchor¸a˙zych 2, 30–084 Krakow, Poland

The ferroelectric materials with perovskite structure are interesting because their physical properties can be easily modiﬁed. Solid solutions based on sodium niobate have ferroelectric and piezoelectric properties. Much interest is paid to the lithum niobate in sodium niobate solid solution. In this paper the temperature changes of pyroelectric current and remanent polarisation of Na1−xLixNbO3 were presented. The pyroelectric measurements were performed in quasistatic method on heating. Remanent polarisation depends on Li-concentration, for x = 0−0,02 it increases, for x > 0,02 – it decreases. It was shown that polar microregions exist in temperature range above Tm.

91 P 22 Tuesday, September 5

The radiation spectrum of an electron moving in a spiral in medium

A.V. Konstantinovich and I.A. Konstantinovich Chernivtsi National University, Department of Theoretical Physics, 2 Kotsyubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

The radiation power for an electron moving in a spiral in transparent isotropic medium are investigated using the improved Lorentz‘s self-interaction method. Using the exact integral relationships for the spectral distribution of radiation power of an electron moving in a spiral in transparent isotropic medium at non-relativistic longitudinal component of velocity (component parallel to magnetic induction vector) the ﬁne structure of the synchrotron-Cherenkov spectrum was investigated by means of analytical and numerical methods. Our numerical calculations of the radiation power spectral distribution were performed at magnetic induction vector Bext = 1 Gs. The performed high-accuracy numerical calculations have shown that the synchrotron-Cherenkov radiation of the electron moving in a spiral in a medium (µ = 1, n = 1.3) is an uniﬁed process. At higher harmonics the maxima in the spectral distribution of the synchrotron-Cherenkov radiation are caused preferably by overlapping between the mth and (m + 1)th harmonics and some contributions of other harmonics.

92 Tuesday, September 5 P 23

Structure and phase transition in pyridazine perchlorate

B. Kostureka, A. Wa´skowskab, S. Dackoa and Z. Czaplaa aWroclaw University, Institute of Experimental Physics, 9 Max Born Sq., 50–204 Wroclaw, Poland, E–mail: [email protected] bPolish Academy of Sciences, Institute of Low Temperature and Structural Research, Ok´olna 2, 50–422 Wroclaw, Poland

Single crystals of pyridazine perchlorate [(C4H4N2) HClO4] have been synthesized and characterized by X-ray diﬀraction, dielectric measurements and optical studies. At room temperature the crystal is monoclinic, space group P21/m. The temperature dependences of the electric permittivity exhibit anomalous behaviour, characteristic of the ﬁrst order phase transition at 343 K and 339 K on heating and cooling, respectively. Optical investigations under polarizing microscope show that on heating the crystal symmetry change is consistent with the transition from the biaxial room-temperature phase II to the optically uniaxial high-temperature phase I. The ferroelastic domain pattern arising after cooling from the phase I points to the rhombohedral-monoclinic transition.

93 P 24 Tuesday, September 5

Phase transitions in Na0.5Bi0.5TiO3–BaTiO3 crystals V.M. Duda, T.V. Kruzina, V.G. Pozdeev and S.A. Popov Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, 49050 Dnipropetrovsk, Ukraine, E–mail: tkruz@ﬀ.dsu.dp.ua

Na0.5Bi0.5TiO3–BaTiO3 (NBT–BT) solid solutions with morphotropic phase boundary (MPB) are very useful as led-free piezoelectric ceramics. However, the position of MPB, number realizable phases and the peculiarities accompanying the phase transitions of NBT–BT do not clear up to present time. The main purpose of this work is the obtaining more information about phase transitions of NBT–BaTiO3 crystals due to investigations of dielectric and optical properties. The crystals of (1 − x)NBT–xBaTiO3 system (x = 0, 0.025, 0.03, 0.032, 0.05, 0.06, 0.13 start mixture) was grown by Czhochralski method. Polarized-optical investigations of domain configurations and transmitted light intensity (wavelength 632 nm) carried out in temperature region 25◦C – 540◦C. The ε = f(t) in crystals of NBT–BT system looks like pure NBT. Therefore, the realization of rhombohedral and tetragonal phases may be proposed. Nevertheless, the anomalies of ε corresponding to these transformations displaced to low temperatures with addition BaTiO3. The dielectric investigations of samples after not long annealing at 600◦C are not indicated the tetragonal-cubic transition. However, polarized-optical investigations shown anomaly of transmitted light intensity at 500◦C for NBT, 440◦C for NBT–0.025BT, 430◦C for NBT–0.03BT, 400◦C for NBT–0.032BT and isotropiza- tion state above. It is reason to supposition of cubic-tetragonal transformation. The observation of domain configurations not contradicts with it and confirms the realization of rhombohedral and tetragonal phase of these crystals. At the same time the cuts of NBT–0.05BT and NBT–0.06BT appeared practical monodomain at room temperature and become isotropic above 180◦C and 200◦C correspondingly. This not correlates with behavior of ε = f(T ). The difference of polarized-optical behavior of NBT–0.05BT, NBT–0.06BT and NBT–0.13BT crystals may be connected with the change of order and character structure distortion which typical for pure NBT. The correlation of dielectric properties, temperature behavior of domain structure and transmitted light intensity is discussed.

94 Tuesday, September 5 P 25

Combined studies for the ferroelectric phase transition in deuterated triglycine sulfate

O.S. Kushnir and R.Y. Shopa Electronics Department, Ivan Franko Lviv National University, 107 Tarnavsky St., 79017 Lviv, Ukraine

We report the results of combined studies for optical birefringence, spontaneous polarization and thermal expansion of deuterated triglycine sulfate (DTGS, deuteration degree x ≈ 0.7) near its ferroelectric phase transition. Critical behaviour in a relatively narrow vicinity of the Curie point is difficult to refer to simple types of logarithmic corrections (see figure 1). Clearly visible fluctuations are also found in comparatively wide temperature interval in the paraelectric phase. Outside the region of notable fluc-

Figure 1: Anomalous part α − α0 of thermal expansion coefficients for DTGS crystals and its cube vs. log of relative temperature modulus. tuations, DTGS manifests deviations from the mean field behaviour (e.g., the averaged critical index β is of the order of 0.4). We have derived quadratic electrooptic and electrostrictive coefficients. The electrooptics and electrostriction effects do not reveal essential nonlinearities (higher order corrections). Our results are compared with the data obtained earlier for the pure TGS, DGTS with the deuteration degrees x different from 0.7 and some other representatives of the TGS family.

95 P 26 Tuesday, September 5

On a correlation between EPR data for SASeD doped with Cr3+ and soft modes

I.E. Lipi´nskia, J. Kuriataa and N.A. Korynevskiib,c aInstitute of Physics, Szczecin University of Technology, Aleja Piast´ow 17, 70–310 Szczecin, Poland, E–mail: [email protected] bInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine cInstitute of Physics, University of Szczecin, Wielkopolska 15, 70–451 Szczecin, Poland

Temperature dependence of the DZZ spin-Hamiltonian parameter, linewidth and integral line intensity is presented for EPR spectrum of Cr3+ doping SASeD single crystal. It is shown that experimentally observed behaviour of the above parameters can be, at least quantitatively understood, in terms of soft modes. The theoretical treatment of points of thermodynamic functions anomalies is based on the two-sublattice model used previously [1–3]. Taking into account interaction between lattice displacements and “spin” subsystems the explicit expression of free energy is obtained. The peculiarities of observed physical properties behaviour are discussed on it’s base.

1. J. Kuriata, I.E. Lipiński, N.A. Korynevskii, T. Bodziony, Physica B 307 (2001) 203– 210. 2. I.E. Lipiński, N.A. Korynevskii, J. Kuriata, W. Pastusiak, Physica B 327 (2003) 116–122. 3. I.E. Lipiński, J. Kuriata, N.A. Korynevskii, M. Soboń, Rev. Adv. Mater. Sci. 12 (2006) 150–153.

96 Tuesday, September 5 P 27

Inﬂuence of the electric ﬁeld E3 and the shear stress σ6 on the ferroelectric phase transition in the KH2PO4 crystal

B.M. Lisnii, R.R. Levitskii and O.R. Baran Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

Within the frame of the proton model that takes into account the short-range and long-range interactions, proton tunneling and piezoelectric coupling [1] we study the influence of the electric field E3 and the shear stress σ6 on the thermodynamics of the ferroelectric phase transition in the KH2PO4 crystal. ∗ The TC − E3 and TC − σ6 phase diagram with critical points E3 = 11917 V/m, ∗ ∗ ∗ TC = 122.77794 K and σ6 = 71349 Pa, TC = 122.77780 K, respectively, are obtained. It is shown that the latent heat depends on the field and stress nonlinearly. We also consider the temperature dependences of the polarization and strain for different values of field and stress. At a field 583.1 kV/m the deviation of the theoretical temperature dependence of the polarization from experimental one [2] reaches 35% and at larger fields this deviation increases.

1. Levitskii R.R., Lisnii B.M. // phys. stat. sol. (b), 241, 1350 (2004). 2. Chabin M., Giletta F. // Ferroelectrics, 15, 149 (1977).

97 P 28 Tuesday, September 5

Dielectric and piezoelectric response of GeS2–Sn2P2S6 glass ceramics

M.M. Maior, I.P. Prits, I.I. Makauz and Yu.M. Vysochanskii Institute of Physics and Chemistry of Solid State, Uzhgorod University, 54 Voloshyna Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected]

Polycrystalline materials like ceramics and composites based on Sn2P2S6 have demonstrated promise as piezoelectric materials for hydrophone application. In this respect glass ceramics on the basis of Sn2P2S6 may be also of interest. The method of preparation of glass-ceramics in the tin hexathiohypodiphosphate system was developed. GeS2 was used for glass formability. Its amount was limited by the optimization of the piezoelectric properties. Their structural and morphological properties were checked by X-ray diﬀraction and scanning electron microscopy. Dielectric and piezoelectric properties of GeS2–Sn2P2S6 ceramics were investigated. The experimental results are compared to the data obtained on Sn2P2S6 based piezoelectric ceramics and composites.

98 Tuesday, September 5 P 29

Dielectric susceptibility of CuInP2(SexS1−x)6 ferroelectrics: does a dipole glass state exist on their phase diagram?

M.M. Maior, L. Beley, M. Gurzan, N. Korda and Yu.M. Vysochanskii Institute of Physics and Chemistry of Solid State, Uzhgorod University, 54 Voloshyna Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected]

Dielectric susceptibility measurements in the frequency range 100 Hz – 10 MHz for the mixed crystals CuInP2(SexS1−x)6 are reported. The x − T phase diagram reveals the following regions with various dipole ordering: at 0.02 ≤ x ≤ 0.05 the phase transition into short-range ordered phase occurs; on other side of the phase diagram at 0.75 ≤ x ≤ 1 the phase transition into long-range ordered phase takes place; at 0.05 ≤ x ≤ 0.75 there is no ferroelectric ordering – the results are interpreted in terms of a possible dipole glass phase in this range of concentrations.

99 P 30 Tuesday, September 5

Electron and hole spectra in quantum wire with two quantum dots in the electric ﬁeld

O. Makhanets, A. Gryschyk and M. Dovganiuk Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, 2 Kotsubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

Modern methods of the epitaxial structures grows opens the perspectives to experimental producing of the complicated nanoheterocompositions consisting of different quantum objects. The nanosystems with double quantum wells are observed thanks to the perspective of their utilization for the creation of infrared range lasers at the inter- band transitions. In the paper the nanoheterosystem consisting of two semiconductor quantum dots (HgS) embedded into the cylindrical quantum wire (CdS) is under research. The quantum dots are tunnelly bound between each other by the barrier-shell (CdS) placed into the stationary electric field directed along the axial axis of quantum wire. The model of rectangular potentials is used for the electrons because the lattice constants of all materials creating the nanoheterosystem are not very different. The electron energy spectrum is obtained in the framework of the effective mass approximation within the solution of stationary Schrödinger equation and using the fitting conditions of the wave function and current of probability density continuity at all interfaces of nanoheterosystem. Numeric calculations of electron energies show that at the increasing of one of quantum dots height, the number of electron energy levels in the quantum well is increasing too and all of them are shifting into the region of smaller energies approaching the bottom of the HgS conductive band bottom. It is established that all energy levels are double degenerated over the magnetic quantum number and the casual degeneration is observed, because at the varying of the quantum well volume the levels with different magnetic quantum number can cross. Anticrossing effect of energy levels with the same symmetry is present in the whole energy region. The magnitude of anticrossing essentially depends on the thickness of barrier shell and characteristics of the electric field.

100 Tuesday, September 5 P 31

Dynamics of the domain structure in non-uniform ferroelectric crystals

K. Matyjasek and R.Z. Rogowski Institute of Physics, Szczecin University of Technology, Al. Piastow 48, 70–310 Szczecin, Poland, E–mail: [email protected]

We report on experimental analysis of the switching polarization in static electric fields and spontaneous depolarization kinetics after removal of the electric fields in non-uniform ferroelectric crystals. We examined telluric acid ammonium phosphate Te(OH)6 · 2NH4H2PO4 · (NH4)2HPO4 and methyloammonium bromobismuthate (CH3NH3)5Bi2Br11 crystals. The switching and backswitching kinetics was investigated by means of the nematic liquid crystal decoration technique in low electric field and switching current registration in high fields. There was observed the essential difference between the domain kinetics observed in inhomogeneous crystals and homogeneous ones. The inhomogeneous crystal consists of independently switched regions, which contribute to the measured switched polarization only if some nuclei within these regions can be activated at given electric field. Thus, the saturation value of the switching polarization increases with the increase of the electric field. In homogeneous crystal samples the switching polarization curves taken at different electric fields typically saturate at the same value, so that they relate to the complete polarization reversal. The temporal relaxation of the polarization during the switching process as well as the spontaneous backswitching process is well described by a Kohlraush-Williams-Watts (KWW) stretched exponential function with the exponent < 1. We have shown that macroscopic inhomogeneity is caused by structural defects in the crystals.

101 P 32 Tuesday, September 5

Dielectric behaviour and pyroelectricity in SBN70–PVC composites

M. Olszowya, Cz. Pawlaczykb, E. Markiewiczb, E. Nogas-Cwikiel´ c and J. Ku lekb aUniversity of Zielona Góra, Institute of Physics, 4 A Szafrana Str., 65–516 Zielona Góra, Poland, E–mail: [email protected] bPolish Academy of Sciences, Institute of Molecular Physics, 17/19 Smoluchowskiego Str., 60–179 Poznań, Poland cUniversity of Silesia, Faculty of Computer and Materials Science, 2 Snie˙zna´ Str., 41–200 Sosnowiec, Poland

Dielectric relaxation of the composites of 0–3 connectivity, made from Sr0.7Ba0.3Nb2O6 (SBN70) ceramic powder and poly (vinyl chloride) (PVC), with the volume fraction of ceramics Φ up to 0.2 was investigated in frequency range 100 Hz – 1 MHz and temperature range 100–450 K. The SBN70-PVC samples in the form of discs with a diameter of 11 mm and a thickness of 200–350 µm were prepared from ceramic and polymer powders by hot-pressing method. The SBN70 ceramic was prepared by a sol-gel route using strontium acetate (CH3COO)2Sr, barium acetate (CH3COO)2Ba and niobium ethoxide (C2H5O)5Nb as precursors. Powders obtained from dried gels were calcined at 870 K for 24 hours to burn off organics. The microstructure of the powders was observed and the grain size was estimated using Hitachi S–4700 scanning electron microscope (SEM). The pyroelectric response investigations were performed using a modified, computer controlled Chynoweth method at room temperature one day after poling. The poled samples were exposed to sine-modulated infrared radiation emitted by a LED diode (λ0 = 0.96 µm, 5 mW) at a modulation frequency from 0.1 Hz to 100 Hz. The SBN70 ceramic modifies the dielectric properties of the PVC polymer: it increases the value of dielectric permittivity in the whole temperature range with some anomaly which is dependent on the volume fraction of the ceramic. The dielectric relaxation time of α process fits to Vogel-Fulcher model. The value of the pyroelectric coefficient p of poled composites depends on the modulation frequency and increases with volume fraction of SBN70 ceramics. The p for composites with the Φ = 0.2 at 1 Hz is about 100 µC/m2 · K. The details of dielectric behaviour and pyroelectricity in SBN70–PVC composites will be presented and discussed in the poster.

102 Tuesday, September 5 P 33

Non-linear optical diagnostic of low temperature semimagnetic phase transitions

K. Ozgaa, A. Slezaka, K. Nounehb,c, I.V. Kitykd,b and S. Benetb aInstitute of Biology and Biophysics, Czestochowa University of Technology, Al. Armii Krajowej 36B, 42–200 Czestochowa, Poland bLaboratoire de Physique Appliquée et Automatique, Universitéde Perpignan, 52 Avenue Paul Alduy, Perpignan, France cGroupe d’Etude des Semiconducteurs, CNRS-UMR 5650, UniversitéMontpellier II, Pl. Eugène Bataillon, 34095 Montpellier Cedex 5, France dInstitute of Physics, Academy J. Dlugosz of Czestochowa, Al. Armii Krajowej 13/15, 42–200 Czestochowa, Poland

Measurements of transport and non-linear optical properties in magnetic semiconductors Pb1−xRxX (R= Pr, Yb and X = S, Se, Te at x ≈ 1−3%) were performed to elucidate an inﬂuence of rare earth ions on behavior of the charge carriers. It was shown that nonlinear optical methods may be used as a sensitive tool for investigation of harmonic and anharmonic electron-phonon interactions near the low temperature semiconductor-isolator phase transformation. The presence of the minimum in Pb1−xPrxTe at about Tρmin = 50 K in the temperature dependence of the resistivity ρ(T ) is due to metal-semiconductor phase transition. Particularly with increasing of electron-phonon interactions indicated by temperature dependent Debye term (parameter b), one can observe an increase of two-photon oscillator strengths.

103 P 34 Tuesday, September 5

Dependence of energy of electronic transition in a quantum dot from symmetry of deformation ﬁeld

R. Peleshchak, O. Dan’kiv and O. Odrekhivs’ka Drohobych Ivan Franko state pedagogical university, 24 Ivan Franko Str., 82100 Drohobych, Lviv region, Ukraine

Today, semiconductor nanoheterostructures are among the key objects of experimental and theoretical physical researches. Nanostructures were successfully used in opto- and microelectronics during last years. For evaluating and controlling the characteristics of semiconductor devices with quantum dots (QDs) and for developing new devices of this type, it is necessary to perform a thorough analysis of the energy spectrum of charge carriers in QDs. It is known that the energy spectrum of electron and hole states is significantly influenced by the elastic strain in QDs. The aim of this article is therefore to research the dependence of energy of electronic transition in a quantum dot from symmetry of deformation field in the framework of the deformation potential model. The results of calculations for the InAs/GaAs heterosystem with InAs QDs. With magnification of the size R0 of a quantum dot the energy of basic optical transition as in case of deformation field of spherical symmetry, and cylindrical symmetry, monotonically diminishes. Set, that in the coherent strain quantum dots of the smaller sizes R0 = (2÷3.2) nm the energy of electronic transition is more in case of influence of deformation field of cylindrical symmetry, than spherical. At R0 > 3.2 nm the opposite effect is observed. Is shown, that the influence of deformation effects on energy of transition in basic state in a quantum dot is more expressed in case of deformation field of spherical symmetry, than cylindrical.

104 Tuesday, September 5 P 35

Self-organizing of defect-deformation structures in crystals within the framework of electron-deformation model

R. Peleshchak, O. Kuzyk and V. Shtym Drohobych Ivan Franko state pedagogical university, 24 Ivan Franko Str., 82100 Drohobych, Lviv region, Ukraine

The theory of formation of nanoclusters and periodic structures of laser-induced point defects that interact with an elastic continuum is previously developed. The interaction of dot lattice defects with self-consistent deformation ﬁeld, caused by dot defects, results in formation of ranked defect-deformation (DD) structures: clusters and periodic structures. The reason of the appearance of non-uniform deformation, which results in local change of band spectrum, is the presence of DD-structures. As a consequence, the spatial redistribution of electrons takes place, which gives birth to electrostatic potential. The criterion of appearance of an n−n+ junction is concentration of lattice defects. At concentration of defects nd0 < ndc1 (nd0 – medial concentration of defects) the processes of self-organizing of defects are absent and, accordingly, a n − n+ junction is absent. Within the interval of concentration of defects ndc1 < nd0 < ndc2 the clusters in crystal are formed, which are the reason of non-uniform deformation. In a result, there is a shortage of electrons in one part of crystal, and surplus – in another. Thus, the double electrical layer is formed in crystal with dot defects. The area of barrier structure becomes sharper and breadth of junction ball diminishes at magniﬁcation of an electron concentration. In irradiated materials, defects are produced as pairs of interstices (θd > 0) and vacancies (θd < 0). Provided that θd > 0, the defects are localized within the region where deformation is positive. If θd < 0, the defects are localized within the region where deformation is negative. At medial concentration of defects nd0 > ndc2 the defect periodic structures are formed. The reason it is served with formation strongly anharmonic periodic DD- structures. Accordingly, redistribution of electrons will have periodic character, and the sequentially joint n − n+ junctions appear. The period of electrical junctions depends on concentration of defects and electrons, and also from elastic constants of crystal.

105 P 36 Tuesday, September 5

Raman studying of K2[Co(H2O)6](SO4)2 crystal I. Polovynko and S. Rykhlyuk Ivan Franko National University of Lviv, Faculty of Electronics, 107 Tarnavs’koho Str., 79019 Lviv, Ukraine, E–mail: [email protected]

The dipotassium hexaaquacobalt(II) sulfate (K2[Co(H2O)6](SO4)2, abbreviation I II KCSH) belongs to compounds, which isomorphous to the M2[M (H2O)6](SO4)2 (where I II M – alkaline metal or NH4, M – divalent metal) and well-known as Tutton’s salts. These salts have been widely investigated and a lot of crystal structures have been reported [1–3]. The purple crystals grown from aqueous solution are monoclinic (space group P 21/a) with unit cell dimensions a = 9.057(1) A,˚ b = 12.211(2) A,˚ c = ◦ 3 6.155(1) A,˚ β = 104.82(1) , Z = 2, Dc = 2.207 Mg/m [3]. The factor group analysis classiﬁed 39 Ag-modes and 39 Bg-modes, which are active in Raman spectra. Other 48 Au-modes and 48 Bu-modes are observed in infrared spectra. Raman spectra of the single KCSH crystal in Z(XY )X, Z(YY )X scattering geometries, which corresponding to Ag symmetry, and Z(XZ)X, Z(Y Z)X, which corresponding to Bg symmetry, have been investigated. 2+ + 2− The title compound is composed of [Co(H2O)6] and K cations and SO4 anions. The Co atom has a slightly distorted octahedral environment, with all positions occupied by oxygen from water atoms. A slightly deformation from the ideal tetrahedral shape around the sulfur is observed. The water molecules and sulphate groups participate in extensive hydrogen bonding lending structural stability of this material.

1. Soboleva L.V., Kirpichnikova L.F. // Crystallography Reports.– 2001.– Vol. 46, No. 2, P. 306–309. 2. Whitnall J.M., Kennard C. // Journal of Solid State Chemistry.– 1977.– Vol. 22, No. 4, P. 379–383. 3. Kirfel A., Klapper H., Schafer W., Schwabenlander F. // Z. Kristallogr.– 1998.– Vol. 213, P. 456–460.

106 Tuesday, September 5 P 37

Tin hexathiohypodiphosphate and analogues: phase diagram, single crystal growth and properties

I.P. Prits, S. Hasynets’, S. Motrya, O. Mykailo, V. Tovt and M. Potorii Institute for Solid State Physics and Chemistry, Uzhgorod National University, 46 Pidhirna Str., 88000 Uzhgorod, Ukraine, E–mail: i [email protected]

Tin hexathiohypodiphosphate Sn2P2S6 and analogues (SnP2S6, CuIn(Cr)–P2S(Se)6, AgInP2S(Se)6) have been widely studied due to its ferroelectric and optical properties but there are no reliable data about type of formation of some ternary and quaternary hypodiphosphates. The Cu2S(Se)–In2S(Se)3–“P2S(Se)4” systems have been established using X-ray diffraction and differential thermal analysis. The phase diagrams of the investigated systems were built on the base of the theoretical and experimental triangulation. CuInP2S(Se)6 tetrary compounds exist in these systems at 770 K in equilibria with binary – Cu2S(Se), In2S(Se)3 and ternary – CuInS(Se)2, In4(P2S(Se)6)3. In order to investigate physical-chemical interactions in CuInS(Se)2–“P2S(Se)4” and CuInP2S6–In4(P2S6)3 systems the corresponding phase diagrams were established. CuInP2S6 forms by syntectic reaction at 1088 ± 5 K and crystallizes in monoclinic space group with cell parameters a = 6.096; b = 10.564; c = 13.623 ◦ (A);˚ β = 107.101 . The CuInP2S6–In4(P2S6)3 system is characterized by eutectic type of interaction. The concentration limits of solid solutions, fixed at the eutectic temperature (1054 ± 5 K), are: for solid solutions based on CuInP2S6 (α) – 48 mol.% In4(P2S6)3; for those based on In4(P2S6)3 (β) – ≈ 10 mol.% of CuInP2S6. CuInP2Se6 melts congruently at 923 K and crystallizes in trigonal space group with cell parameters: a = 6.397(4), c = 13, 341(3) (A);˚ Z = 2. Investigation of the phase equilibria in SnS2–PS system indicates the existence of narrow homogeneity region on the Sn2P2S6 base with temperature maximum – 1070 ± 5 K. Studying of the interaction in AgInP2S6–AgInP2Se6 system shows complete miscibility in both solid and liquid states. Single crystals of Sn2P2S6, Pb2P2S6, Sn2P2Se6, Pb2P2S6 (with sizes 8 × 8 × 5 mm), CuInP2S6, CuInP2S6, CuCrP2S6 (platelets with sizes 10 × 8 × 0.1 mm) and their solid solutions were grown by chemical vapor transport (CVT). Large single crystals ( = 14−16 mm, l = 20−25 mm) of these individual compounds and AgInP2S6, AgInP2Se6 were grown by Bridgman technique. The dielectric and optical properties of crystals, ceramics and composites based on investigated materials have been determined.

107 P 38 Tuesday, September 5

Tin hexathiohypodiphosphate single crystal growth

I.P. Prits, I. Stoika, M. Gurzan, Yu.Yu. Gaza and M.M. Danko Institute for Solid State Physics and Chemistry, Uzhgorod National University, 46 Pidhirna Str., 88000 Uzhgorod, Ukraine, E–mail: i [email protected]

For the purpose of improving photorefractive properties of Sn2P2S6 the new crystals were obtained by chemical vapor transport (CVT) and Bridgman technique using nonstoichiometric Sn2P2S6 and compositions with an additional amount of the tellurium (up to 1 mol.%). The technological conditions of CVT process are given in Table 1.

No. Growth am- Transport. Temperature, Results poule size, concentr., hot zone/cold /l, mm mg/sm3 zone, K 1. 24/150 1 860/850 isometric crystals 2. 26/160 1,5 880/865 well developed faces 3. 28/170 2 870/855 rhombic bipi- ramide 4. 30/180 2,5 860/840 round crystals 5. 32/170 2 890/880 round crystals

In result there were obtained dark-red single crystals with the size 10 × 10 × 12 mm3 with high optical quality and diﬀerent habitus. The experience of the Sn2P2S6 single crystals growth by Bridgman method using stoichiometric Sn2P2S6 or composition corresponding to temperature maximum of this compound, shows low optical quality of the obtained crystals. In order to remove this problem, connected with speciﬁc of the Sn2P2S6 microdiagram, the single crystals of the several compositions (95 mol.% Sn2P2S6 – 5 mol.% SnS; 90 mol.% Sn2P2S6 – 10 mol.% SnS; 95 mol.% Sn2P2S6 – 5 mol.% SnS2; 95 mol.% Sn2P2S6 – 5 mol.% “P2S6”) with the sizes – = 14 mm, l = 30 mm, have been grown using direct crystallization (Table 2).

Temperature of melt zone 1130 K Temperature of annealing zone 850 K ∆T 3–4 K/mm Transfer speed 2.5 mm/day Cooling speed of crystal 200 K/day

The best result was obtained on the crystal, formed in Sn2P2S6–“P2S6” system, others were “milky”. The optical properties of the new Sn2P2S6 crystals were investigated.

108 Tuesday, September 5 P 39

Three-dimensional Ising-like system in an external ﬁeld: Microscopic calculation of the free energy in the higher non-Gaussian approximation

I.V. Pylyuk Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

The Ising model is widely used in the theory of phase transitions for the study of properties of various magnetic and nonmagnetic systems (ferroelectrics, ferromagnets, binary mixtures, etc.). The analytic method for deriving the total free energy of a three-dimensional Ising- like system near the critical point in a homogeneous external field is developed in the ρ6 model approximation. This higher non-Gaussian approximation is based on the sextic distribution for modes of spin-density oscillations [1]. The main distinctive feature of the proposed method is the separate inclusion of the contributions to the free energy from the short- and long-wave spin-density oscillation modes. Mathematical description proposed for temperatures T > Tc (Tc is the phase-transition temperature in the absence of an external field) is valid for fields near h˜c, where the scaling variable is of the order of unity and power series in this variable are not effective. The limiting field h˜c satisfies the condition of the equality of sizes of the critical-regime regions by the temperature and field (the temperature and field effects on the system in the vicinity of the critical point are equivalent) [2,3]. The generalized point of exit of the system from the critical regime contains both the temperature and field variables. The expression for the total free energy is obtained as a function of these variables and microscopic parameters of the system without using series expansions in the scaling variable. The free energy includes the terms, which determine the temperature and field confluent corrections.

1. I.R. Yukhnovskii, M.P. Kozlovskii, and I.V. Pylyuk, Phys. Rev. B 66, 134410 (2002). 2. I.V. Pylyuk, M.P. Kozlovskii, and O.O. Prytula, Ferroelectrics 317, 43 (2005). 3. M.P. Kozlovskii, I.V. Pylyuk, and O.O. Prytula, Phys. Rev. B 73, 174406 (2006).

109 P 40 Tuesday, September 5

Internal friction in the Sn2P2S6 ferroelectric I.M. Rizaka, V.S. Bilanychb and V.M. Rizakb aDnipropetrovsk National University, Dnipropetrovsk, Ukraine bUzhgorod National University, Uzhgorod, Ukraine, E–mail: [email protected] The studies of the processes of slow variation of the order parameter in the 24 Sn2P2S6-like crystals by the internal fric- 0,08 2 tion method have shown that the me- 22 chanical losses in this crystal in the regi- 0,06 -1 on of the phase transition (PT) are low- Q frequency ones, while the increase of the 0,04 1 20 GPa G, amplitude of external exciting ﬁeld results in the increase of inelastic deforma- 0,02 24 tions and washing out the II-order phase 320 360 400 transition (336 K) [1]. The goal of this 0,08 T,K work was to study the inﬂuence of irradi- 22 0,06 ation on the mechanical properties of the -1 4

Q Sn2P2S6 crystal. 0,04 3 Irradiation was carried out at the radi- 20 GPa G, ation bench of an M-30 microtron at the 0,02 Institute of Electron Physics, Ukrainian 18 320 360 400 NAS. The energy of the bremsstrahlung T,K gamma-quanta was 15 MeV, the absorbed dose was 2.47 · 105 Gy. The accuracy of dose determination was 6%. The mechanical properties were studied by measuring the internal friction Q−1 and shear modulus G at the 10−3−10−1 Hz frequencies. Figure shows the Q−1(T ) and G(T ) dependences at the 3 · 10−5 relative deformation amplitude (3, 4 – those for irradiated crystal). It has been found that radiation influence influences effectively the mechanical properties of this crystal. In particular: (a) the shape of the G(T ) dependence in the PT region and in the paraphase changes considerably, at the transition from the ferrophase to the paraphase a shear modulus leap is observed as well as its non-monotonous critical behavior at the PT point, while the anomaly in G(T ) in the PT region becomes more expressed, i.e. classical; (b) mechanical losses Q−1 in the PT region increase considerably, ad additional “leg” appears in the maximum of the inner friction within the 340–360 range. Irradiation of the crystal results in the general reduction of the shear modulus in the paraphase, while in the ferrophase it remains unchanged. All the anomalies in Q−1 and G are localized in the 320–365 K temperature interval. The influence of irradiation on the inner friction mechanisms in Sn2P2S6 are discussed. 1. V.M. Rizak, I.M. Rizak, V.S. Bilanych, I.P. Prits. Infralow-Frequency Mechanical Properties of Sn2P2S6 Single Crystal. // Ferroelectrics, v. 6, N 1, 2004, p. 157–162.

110 Tuesday, September 5 P 41

Ab initio calculation of vibrational and electronic spectra of Sn2P2S6 ferroelectric crystals I.M. Rizaka, O.I. Chobalb and V.M. Rizakb aDnipropetrovsk National University, Dnipropetrovsk, Ukraine bUzhgorod National University, Uzhgorod, Ukraine, E–mail: [email protected]

Two-valence metal hexatiodiphospites have important applied significance and are characterized by the presence of several polymorphous forms, transitions between them can be initiated by the thermal effects and photoeffects and are accompanied by the structural changes, which can be detected by the type of vibrational spectra. In this paper, using the restricted Hartree-Fock (RHF) method the quantum- mechanical calculations of equilibrium structure, electron structure, infrared vibrational spectra and Raman spectra for structural units of the Sn2P2S6 crystals: the 4− [P2S6] anion and the Sn2P2S6 molecule have been carried out. Within the framework of quasi-molecular cluster method, the form of the adiabatic potential for the ferroelectric Sn atom has been calculated. The Sn8P8S24 cluster was used for calculations since it is the minimal cluster, which reproduces the chemical bonding and the local (i.e. determined by this bonding) properties. All calculations have been carried out by means of the PC GAMESS code of the GAMESS (US) quantum-chemical software using the basis set 3-21++G**. The results obtained testify that in conditions of geometry optimization the molecular model under study keep the topology of the modeled crystal Sn2P2S6, while calculated frequency and geometric parameters values are close to relevant experimental ones for the crystal. Calculated local potential has a form of a single-well potential that allows ferroelectric phase transition in the Sn2P2S6 crystals to be classified as the displacement-type phase transition.

111 P 42 Tuesday, September 5

Properties of doped bismuth tellurite single crystals

L. Sadovskaya and K. Agarkov Dnipropetrovsk National University, Department of the solid state physics, 13 Naukovaya Str., 49050 Dnipropetrovsk, Ukraine, E–mail: agarkov@ﬀ.dsu.dp.ua

Bi2TeO5 (bismuth tellurite) is one of the stable forms among the compositions identified in Bi2O3 – TeO2 system. The crystal symmetry predicted nonlinear properties which were experimentally confirmed. The crystal became important when its interesting photorefractive properties were reported. The dopants influence on the photorefractive and other properties. In this work we discuss the information in the growth and investigation of doped Bi2TeO5 crystals. Fe, Cr, Mn doped crystals were growth by the Czochralski technique. These dopants were added to the melt in the oxide form in concentration of 10−3 mole of host. The absorption spectra were obtained from transmission and reflection spectra. The undoped Bi2TeO5 crystals were pale yellow in color and transparent in the visible and near infrared range 0.38–0.7 µm. The temperature dependence of the spectra was followed and analyzed in the 300–400 K regions. Optical samples with thickness from 2 mm to 25 µm were prepared by cleaving along the (100) plant. The absorption spectra of the doped Bi2TeO5 crystals were investigated at room temperature. It must be emphasized that among investigating dopants the Cr influenced clearly absorption spectrum of the host materials. Pronounced peak were investigated in the absorption spectra of the Cr doped crystals in the range from 2,4 to 3 eV. The influence of the specific dopants on the optical and electrical characteristics is discussed.

112 Tuesday, September 5 P 43

Eﬀect of Ni substitutional impurities on the electronic properties of the ferroelectric SbSI crystal

D.M. Berchaa,b and I.V. Slipukhinaa aInstitute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyn Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected] bInstitute of Physics, University of Rzesz´ow, Rejtana 16a, 35–310 Rzesz´ow, Poland, E–mail: [email protected]

The V-VI-VII-group single crystals like SbSI are promising photoferroelectric materials with semiconducting properties. The temperature of the ferroelectric phase transition in these compounds strongly depends on their purity. Moreover, the experimental observations point at the significant changes in optical and electrical properties of doped V-VI-VII-group ternary compounds. Since there is a lack of theoretical in- terpretation of the existing experimental results on the investigation of physical and chemical properties of such systems doped with transition-metal atoms, we have performed completely ab initio studies of the influence of Ni substitutional impurities on structural, electronic and magnetic properties of the ferroelectric semiconducting SbSI crystal. First-principles structural relaxation in a supercell approximation revealed a five-fold distorted square-pyramidal coordination of the defect atom in the host material. The calculated spin-polarized electronic band spectrum shows that the substitution of Sb3+ by Ni2+ ion results in additional non-degenerate defect states localized within the forbidden gap. Our calculations show that the doped SbSI crystal is a semiconductor with an indirect band gap. The calculated combined density of states qualitatively correlates with the known results on impurity optical absorption measurements. The Mülliken population analysis revealed the existence of a total magnetic moment of the cell of about 1 µB and showed that the configuration of substitutional Ni in SbSI is compatible with 3d7. The obtained non-integer values for the d-orbital population point at the strong p − d hybridization in the system.

113 P 44 Tuesday, September 5

Pyroelectric properties of TGS crystals doped with metal atoms

A.G. Slivka, V.M. Kedyulich and A.I. Susla Uzhhorod National University, Optics Department, 54 Voloshyn Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected]

Physical properties of real crystals can be essentially affected by defects and impurities. By means of technologically controlled doping with impurities of various type one can optimize physical and technical parameters of materials and, hence, improve the parameters of optoelectronic devices. Here we present the results of experimental studies of temperature dependence of dielectric permeability, pyroelectric current and dielectric loss angle tangent for TGS crystals doped with Cr3+ ions. Temperature dependences of spontaneous polarization, pyroelectric coefficient, and figures of merit (M1, M2, M3) for TGS: Cr3+ crystals are analyzed. Doping of TGS with Cr3+ ions is shown to result in considerable improvement of its pyroelectric figures of merit.

114 Tuesday, September 5 P 45

The structural and dielectric properties of the Na0.96Li0.04NbO3 ceramic W. Smiga´ a, B. Garbarz-Glosa, G. Stopaa, J. Suchanicza, M. Dambekalneb, A. Stenbergb and Cz. Ku´sa aInstitute of Physics, Pedagogical University, Podchor¸a˙zych 2, 30–084 Krakow, Poland bInstitute of Solid State Physics, University of Latvia, Kengeraga 8, LV–1063, Riga, Latvia

+1 +5 The sodium niobate Na Nb O3 is the perovskite ABO3-type compound. It has ferroelectric, antyferroelectric or paraelectric properties in diﬀerent temperature ranges. Some solid solutions based on NaNbO3 have ferroelectric and good piezoelectric properties. Lithium niobate – sodium niobate solid solutions are very interesting. Ceramic samples Na0,96Li0,04NbO3 were obtained by means of conventional ceramic technology in the Institute of Solid State Physics at the University in Riga (Latvia). Bored on rentgenostructural measurements, the investigations were performed in order to denote the crystal structure the phase and structural analysis was performed and the lattice constants were denoted. It follows, that the lattice parameters and the volume of the unit cell for Na0,96Li0,04NbO3 decreased in comparison with pure NaNbO3. The microstructure and EDS measurement have been performed by means of scanning electron microscope. The dielectric and hysteresis loops measurements of Na0,96Li0,04NbO3 have been also carried out. The dielectric measurements were performed in heating and cooling processes in the range of frequencies 100 Hz – 20 kHz, for temperatures 300 K – 750 K, without and under axial pressure up to 120 MPa. It has been stated, that the maximum of electric permittivity ε(T ) becomes more diffused with the increase of axial pressure and the temperature of phase transition Tc decreases. The value of tan δ increases with the increase of axial pressure and its local maximum shifts towards lower temperatures.

115 P 46 Tuesday, September 5

The conditions of the passage of phase equilibrium curve into the supercritical curve of lowered stability in the ferroelectric Lieb model

E.D. Soldatova and A. Galdina Dnipropetrovs’k national university, Faculty of physics, 13 Naukova Str., 49050 Dnipropetrovs’k, Ukraine, E–mail: galdina@ﬀ.dsu.dp.ua

The conclusion of variety of critical state manifestations is based on combination of limit properties of subcritical and supercritical states. It was interesting to investigate the conditions of the passage of subcritical phase equilibrium curve into the supercritical curve of the lowered stability. Such a consideration is carried out on the basis of examination of stability requirements. The basic stability characteristics of a system are the determinant of stability D and the stability coefficients (the SC’s). These quantities are inversely proportional to fluctuations of external parameters of the system. At the continuous transitions D and the SC’s pass finite minima, that corresponds to the growth of fluctuations. The locus of these minimum is curve of supercritical transition (the lowered stability curve or quasispinodal). The limit case of these continuous transitions, when fluctuations in the system are at the high and D and the SC’s pass zero minima, is the critical state. The critical point is also the limit point of some first-kind transition (the limit point of phase equilibrium curve). On the quasispinodal the next condition is fulfilled:

∂D ∂D dD = dS + dx = 0. (1) ∂S !x ∂x !S Here X is generalized thermodynamic force, x is conjugated variable and S is an entropy. Then on the T − X plane the equation of quasispinodal takes the form dT = f(S, x) = const. dX In the paper the ferroelectric Lieb model is considered. As it is revealed, the equation of quasospinodal for this model is E = 0, i.e. the maximal growth of ﬂuctuations is observed under zero electric ﬁeld. The critical slope of the subcritical phase equilibrium curve is Kc = 0. It means, that for Lieb model it is realized the case of continuous passage of the equilibrium curve into the lowered stability curve because of the same critical slopes.

116 Tuesday, September 5 P 47

Dynamic susceptibility of proton-glass model with essential short-range interactions

S.I. Sorokov, R.R. Levitskii and A.S. Vdovych Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected]

A Glauber dynamics of the proton-glass model with essential short-range competing interactions (the first coordination sphere with random distribution of the interaction parameter is taken into account) and weak long-range interactions is investigated within a symmetric replica approach. A system of equations for the distribution function of static effective fields and linear response of the effective fields are derived within the cluster approximation, and Gauss solutions are obtained. The temperature dependence of the dynamic susceptibility and effective relaxation time is investigated. In the spin-glass region the imaginary part of the susceptibility has a high temperature peak (beginning of the glass phase) and a low temperature peak (corresponds to the freezing line). Influence of the long-range interactions and random internal fields on the phase diagram and dynamic characteristics of the model is studied. Applicability of the theory for description of relaxation properties in proton-glasses of the Rb1−x(NH4)xH2PO4- type is discussed.

117 P 48 Tuesday, September 5

The optical properties of mechanically clutched TGS crystals with L-valine admixture

V.Yo. Stadnyka, M.M. Romanyukb and J. Stankowskac aLviv Ivan Franko National University, 79005 Lviv, Ukraine, E–mail: [email protected] bLviv Polytechnic National University, Lviv, Ukraine cPoznan Adam Mickevich University, Poznan, Poland

In this work we study the influence of L-valine admixture (CH3)2-CH-CHNH2COOH (L-valine) upon the birefringent and piezooptic properties of the TGS crystals. The temperature and spectral dependences of the 4ni were measured with the interference technique. It was determined that the 4ni value increases linearly up to the stresses of σm ≈ 200 bar. The σx and σy stresses lead to different values and signs of the nz changes, −5 −5 namely, we have δ4nz = −7.2·10 (at σy = 200 bar) and +8.1·10 (at σx = 200 bar). The corresponding dependences of 4nx and 4ny are quite similar. In general, one of the stresses normal to the propagation direction always imposes an increase in the 4ni, while the other one leads to the opposite. Furthermore, those increments appear to be different in module (δnx > δny ≥ δnz). The general features are as follows: (1) the 4ni changes are proportional to temperature, (2) the derivative ∂4ni/∂T changes its value while passing through the Curie point, (3) the uniaxial stresses change the absolute value of 4ni, though remain a qualitative temperature character of 4ni unchanged, and (4) the PT point is shifted under the influence of the stress. x The PT temperature decreases for the cases of σx and σy stresses (Tc = 320.5 K and y z Tc = 320.2 K), while the σz stress increases the PT point (Tc = 325.2 K). The relevant temperature shift coefficients are equal to ∂Tc/∂σx = 0.0064, ∂Tc/∂σy = −0.0080 and ∂Tc/∂σz = 0.0171 K/bar. The “total” (or hydrostatic) coefficient for the PT temperature shift is +0.0027 K/bar. Those PT shifts have been explained by influence of temperature and stresses on the shifts of structural elements taking place for the PTs. Those slight discrepancies may be caused by both a complex structure of TGS crystals and possible irregularities of introducing the valine admixture into the crystal structure. While the crystal doped with L-valine is growing, the admixture enters into the structure by means of substituting one of the glycines. When the L-valine molecule substitutes the glycine I, the spontaneous polarization Ps becomes fixed and a biasing field appears, altering all the dielectric parameters of crystals and shifting the PT point. Moreover, a notable shift in the PT point towards higher temperatures should be apparently caused by the influence of uniaxial stresses upon the ferroelectric domains.

118 Tuesday, September 5 P 49

The baric changes of the refractive properties of K2SO4 crystals

V.Yo. Stadnyk, M.O. Romanyuk, O.Z. Chyzh and V.F. Vachulovych Lviv Ivan Franko National University, 79005 Lviv, Ukraine, E–mail: [email protected]

The aim of this work is to study the birefringence 4ni of K2SO4 crystals in wide spectral (300–800 nm) ranges, as well as an inﬂuence of uniaxial mechanical stresses on the birefringence properties. K2SO4 crystals were grown by a slow evaporation of an aqueous solution. The grown crystals were a good optical quality and had a orthorhombic form. The spectral dependences of the ni were measured with the interference technique. The uniaxial mechanical pressure was applied with the aid of a special device, allowing application of stresses as large as ≈ 500 bar. The dispersion of the birefringence 4ni is normal in the whole spectral interval of investigation. The spectral dependences of the birefringence are in a good agreement with relevant dependences for the refractive indices ni of the crystals concerned. A comparison of 4ni with corresponding values for LiRbSO4 and LiKSO4 isomorphous crystals showed that the cation substitution Rb+ → K+ in the sublattice results in a birefringence growth by 0.008–0.010 on the average, while the Li+ → K+ and Rb+ → + Li substitutions result in an average decrease of 4ni by 0.02 and 0.03, respectively. The results are primarily due to the variations of the refractive indices, to the shifts of UV and IR absorption bands, and to the changes of relevant additive refractions and electron polarizability. The values of 4ni for this crystal are sensitive to the uniaxial stress action and −4 change almost linearly with the stress as follows: 4nz : δ4nz = +1.15 · 10 and −4 −1.80 · 10 (for σx and σy = 100 bar, respectively). In general, although mechanical stresses aﬀect the 4ni values, they do not change substantially their dispersion. It was found that if the uniaxial stress is X-directed, then 4nz increases and 4ny decreases, for Y -directed, then 4nx increases and 4nz decreases. Since a relation nx > nz > ny between the refractive indices and 4nx = nz − ny, 4ny = nx − nz and 4nz = nx − ny between the birefringence of K2SO4 crystals was established than concluded the increasing of the anisotropy of optical indicatrix under σm uniaxial stress action. It was studied by extrapolation of lines 4ni = f(σm) and solving the solution −3 4nz|σ=0 +b1σx = 4nx|σ=0 − b2σz that the equality 4nz ≈4nx ≈ 3.49· 10 at stresses σz ≈ σx ≈ 1.66 kbar of K2SO4 crystal. It means that the application of the uniaxial stress leads to appearing of the pseudo-isotropic point of K2SO4 crystal.

119 P 50 Tuesday, September 5

The inﬂuence of the mechanical pressure on the infrared spectra of (NH4)2SO4 crystals V.Yo. Stadnyk, M.O. Romanyuk and M.R. Tuzyak Ivan Franko Lviv National University, 79005 Lviv, Ukraine, E–mail: [email protected]

The aim of this work is to study the effect of uniaxial mechanical stresses on the infrared spectra with the purpose of further ascertaining their selective influence upon dynamics and spatial orientation of individual structural elements of the sulfate ammonium (NH4)2SO4 (SA) crystals. It is revealed that two distinct bands with the maximums at 1155 . . . 1164 (the most intensive band II) and 1445 . . . 1461 (the band III) cm−1 are present in the above range of the reflection spectra for the three polarizations. The tetrahedral structure has the symmetry Td and 9 internal modes: single longitudinal (ν1), double transverse (ν2), triple longitudinal (ν3) and triple transverse (ν4), among which only ν3 and ν4 are active −1 −1 in the IR region. The modes ν2 = 968 . . . 986 cm and ν3 = 1155 . . . 1164 cm corre- −1 spond to the vibrations of SO4 tetrahedron, while the mode ν4 = 1445 . . . 1461 cm to the vibrations of NH4 tetrahedron. It is shown that significant changes in the IR reflection spectra take place if the crystal is subjected to uniaxial pressure along the crystal physical directions. Namely, the changes in both the intensity and the maximums positions occurs for the main reflection peaks. So, the intensity of the band II decreases about 10% for the case of the light polarization EkX and the uniaxial pressure σx, while the corresponding maximum shifts towards the lower-energy side by −1 −4 ∂ν3 ≈ 5 cm for σx = 100 bar and we have ∂λ3/∂σ ≈ 4 · 10 µm/bar. Similar baric −1 dependences are revealed for the band III: the long-wavelength shift by ∂ν3 ≈ 4 cm . In case of the light polarization EkY and the uniaxial pressure σy the intensity of the band II also decreases, whereas its maximum shifts towards the higher-energy side −4 ∂λ3/∂σ ≈ 3 · 10 µm/bar. On the basis of the dispersion Kramers-Kronig relations, the reflection spectra enable one to obtain baric changes in the spectral dependences of optical constants of the SA (the refractive index n, the real (ε1) and imaginary (ε2) parts of the dielectric permittivity) along the crystal physical axes. A rapid increase of the refractive index is detected inside the absorption bands. The variations of the refractive index outside the absorption bands corresponds to the normal dispersion (∂n/∂λ < 0). Using the calculated dispersion curves of the real (ε1) and imaginary (ε2) parts of the dielectric permittivity, we have determined the frequencies of longitudinal vibrations ωLO as mi- nimums of (ε1) function and the frequencies of transverse vibrations ωTO as maximums of (ε2) function for mechanically free and clamped crystals.

120 Tuesday, September 5 P 51

The band energy structure of RbKSO4 crystals O.V. Bovgyra, V.Yo. Stadnyk, A.V. Franiv, M.R. Tuzyak and O.Z. Chyzh Ivan Franko Lviv National University, 79005 Lviv, Ukraine, E–mail: [email protected]

In this work we report the results of theoretical ab initio calculations for the energy band structure and the imaginary part ε2 of complex dielectric permittivity of single RbKSO4 crystals in their monoclinic paraelectric phase. When performing non-local calculations of the band-energy spectra E(k) within the theory of electronic density functional, we have used non-singular norm-preserving scalar-relativistic pseudo- potentials by Bachelet-Hamann-Schluter. Plane waves have been used as the basic function system. Crystalline structure has been determined with the powder technique on the basis of diﬀractometer HCG-4A. It has been revealed that RbKSO4 crystals belong to the rhombic syngony and are characterized by spatial group Pnma, with the cell parameters a = 7.5526(4) A,˚ b = 5.8048(3) A,˚ c = 10.1156(6) A˚ and the following atomic distributions: O1 at 8(d) x y z (x = 0.3080, y = 0.0430, z = 0.1530), O2 at 4(c) x 1/4 z (x = 0.0450, z = 0.830), Rb at 4(c) x 1/4 z (x = 0.1728, z = 0.4100), S at 4(c) x 1/4 z (x = 0.2324, z = 0.0815), K at 4(c) x 1/4 z (x = 0.4895, z = 0.7048), and O3 at 4(c) z 1/4 z (x = 0.7930, z = 0.5580), where the reliability factor is R = 0.09. The elementary cell volume is equal to 441.6(1) A˚3 and the crystal density is 2.8055(6) g/cm3. RbKSO4 crystals have the elementary cell structure peculiar for the crystals of β- K2SO4 group. Tetrahedral carcasses united into six-fold circles, whose vertices can be turned down or up along c axis are determinative motives of that structure. Such the cell types are characterized by pseudo-hexagonality and speciﬁc “triples” in the grown crystals. The elementary cell of RbKSO4 crystal involves four formula units. It is ascertained that the top of the valence band (the energy level 0 eV) is localized at the point D(k = (0.5; 0.5; 0)). The bottom of the conduction band is located at the point Γ. The least direct forbidden gap (the point Γ) amounts 8.80 eV. However, one should keep in mind a usual underestimation of the energy gap peculiar for the calculations performed in frame of the local density approach. The valence complex of single RbKSO4 crystals consists of separate narrow band “bindings” separated by forbidden gaps. The top of the valence band is formed by the connecting p-orbitals of sulfur. The bottom of the conduction band is mainly formed by the s and p-states of K and Rb hybridized with anti-connecting p states of S and O. Thus, the fundamental optical absorption is mainly caused by intra-anionic transitions.

121 P 52 Tuesday, September 5

Equilibrium states and phase transitions in the crystals possessing chain structures with hydrogen bonds

I.V. Stasyuk and R. Stetsiv Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine,E–mail: [email protected]

The possibility of the ﬁrst- or the second-order transitions from uniform phase into phase with the doubled lattice period is studied in framework of pseudospin-electron model, proposed for the description of the proton-electron interactions in quasi-one- dimensional structures with hydrogen bonds. The Hamiltonian of the model includes terms which indicate correlation between the proton displacement along bond and re- construction of electron states, as well as change their occupancy. Besides that Hamil- tonian of the model includes terms which describe the tunneling hopping of proton, electron transfer and asymmetry of the local anharmonic potential. Anharmonicity of the motion of protons on hydrogen bonds is described by the pseudospin formalism. The dependence of the electron concentration and average pseudospine values on chemical potential and asymmetry ﬁeld were obtained. The electron spectrum is calculated. The equation for the phase transition temperature is obtained. The phase transition lines from the uniform phase into phase with the doubled lattice period is determined. The possibility to use of model to the description of quasi-one-dimensional structures so called halogen-bridged mixed-valence metal complexes [1] is discussed.

1. K. Okaniwa, H. Okamoto, T. Mitani, K. Toriumi and M. Yamashita, J. Phys. Soc. Japan, vol. 60, No. 3, p. 997 (1991).

122 Tuesday, September 5 P 53

Photochromic eﬀect and induced photocondactivity in undoped and doped sillenite bismuth crystals

K. Strelets and T. Panchenko Dnepropetrovsk National University, Faculty of physics, 13 Naychnaya Str., 49050 Dnepropetrovsk, Ukraine, E–mail: [email protected]

Photoinduced phenomena in the crystals of sillenite family Bi12MO20 (with M = Si, Ge, Ti) are strenuously studied, because this crystals are been used as us functional media in different types on light-modulating devices. So the investigation of influence of dopes of properties of these materials have interest for miens of modification and for understanding of mechanism of the photoinduced phenomena. The results of investigation of induced photoconductivity (IP) and photochromic effect (PCE) of Cu, Ag and Mo doped Bi12MO20 (BSO) crystals are present in this report. Single crystals were grown by Czochralski technique, the content of an impurity in crystals was ≈ 0.1 wt.%. Spectra of an optical absorption and photoconductivity are investigate in the wavelength range from 4 µm to 0.35 µm. PCE and IP are excited by light in a blue-green range of the spectrum. The influence of temperature on thermal discoloration are investigated also. It is shown, that for spectral regions 2.2–3.4 eV (A) and 0.5–2.2 eV (B) the following features are characteristic. Illumination from A-range causes both effects, PCE and IP, here the spectrums of their excitation are identical and have a sharp border 2.2 eV. Illumination from B-range destroy of PCE and partial optical extinguishing of photoconductivity are observed. The received results are discussed with attraction of semiempirical variant of the theory of a crystalline field of ligand and also model of multicentral recombination. It is shown, that despite of a generality of causes of excitation and destruction, PCE and IP have essentially the various nature. PCE it is caused by optical recharge of color center in accordance with mechanisms: Cu3+ + e −→ Cu2+, Ag+ − e −→ Ag2+, 6+ 5+ Mosi + e −→ Mosi . The IP effect, opposite, is caused, mainly by filling of shallow levels joining to a bottom of conductivity band and a ceiling of a valency band.

123 P 54 Tuesday, September 5

Temperature behaviour of order parameter in Cu6PSe5I(Br) superionic conductors I. Studenyaka and M. Kranjˇcecb aUzhhorod National University, Faculty of physics, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected] bUniversity of Zagreb, Faculty of Geotechnics, 7 Hallerova Aleja, 42000 Varaˇzdin, Croatia, E–mail: m [email protected]

Cu6PSe5I(Br) crystals belong to argyrodite family characterized by dense tetrahedral packing of phosphorus and sulphur atoms and partial population of systems of equivalent positions by copper atoms. The latter results in the order-disorder type phenomena, phase transitions and high ionic conductivity. At room temperature these crystals, similarly to Cu6PS5I(Br), belong to cubic syngony (F 43m space group), and at low temperatures an isostructural superionic phase transition takes place at Ts = (263 ± 1) K for Cu6PSe5I and Ts = (259 ± 1) K for Cu6PSe5Br. Long-wavelength fundamental absorption edge of Cu6PSe5I(Br) crystals in the non- superionic (T < Ts) and superionic (T > Ts) phases is of Urbach shape. In the range of ∗ the superionic phase transition a stepwise behaviour of optical pseudogap Eg and an anomalous change of the absorption edge energy width w are observed. From the experi- ∗ mentally obtained temperature dependence of optical pseudogap Eg (T ) the pseudogap ∗ increment ∆Eg (T ) in the low-temperature phase with respect to the high-temperature one was calculated. The optical pseudogap values in the low-temperature phase were obtained by extrapolation of the experimental dependence in the high-temperature ∗ phase to the low-temperature one using the Einstein model. By expansion ∆Eg (T ) into a series of even degrees of the order parameter η(T ) and restricting the expansion to the ﬁrst term, temperature dependences of the order parameters of the phase transition were obtained. The obtained dependences for Cu6PSe5I(Br) crystals appeared to be typical for the ﬁrst-order phase transitions.

124 Tuesday, September 5 P 55

Phonon spectra of Cu6PS5Br superionic ferroelastic: experimental and theoretical studies

I. Studenyak, K. Rushchanskii and V. Stephanovich Uzhhorod National University, Faculty of physics, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine, E–mail: [email protected]

A superionic ferroelastic crystal Cu6PS5Br possesses icosahedric structure of ar- gyrodyte type. This crystal undergoes a superionic phase transition (PT) at Ts = 166−180 K and a ferroelastic phase transition at Tc = 268 ± 2 K. The ferroelastic PT is a second order transition, as indicated by a typical temperature behavior of speciﬁc heat, dielectric constant and elastic properties. At T = Tc domains appear in the crystal structure. At room temperature (T > Tc) the crystal has cubic structure (space group F 43m). Below the ferroelastic PT temperature Cu6PS5Br crystals belong to monoclynic syngony (Cc space group), and the superionic PT reveals the features of an isostructural transformation. Cu6PS5Br single crystals were grown using chemical vapour transport method. Ra- man scattering measurements were performed at room temperature on a LOMO DFS- 24 grating monochromator, the excitation being provided by a He-Ne laser (632.8 nm). In the Raman spectrum of single crystal separate groups of bands are observed. In the low-frequency range (below 100 cm−1) the bands corresponds to diﬀusive-type vibrations of Cu atoms and Cu-Br bond vibrations are observed. In the range near 310 cm−1 a broad asymmetric band is observed, which results from the superimpose- −1 ment of a doubly degenerate P X mode and a triply degenerate F2 mode. At 425 cm in the Raman spectra the band, corresponding to A1 symmetry vibration, is observed, being the most pronounced in the spectra. In the range 500–600 cm−1 two bands are observed in the spectra, related to TO and LO vibrations of F2 mode, corresponding 3− to internal stretching vibrations of PS4 tetrahedral groups. Using density functional perturbation theory within local density approximation an ab initio phonon spectrum over entire Brillouin zone have been obtained for high- symmetry cubic structure. In phonon spectrum two unstable mode indicating the experimentally observed sequence of ferroelastic and superionic phase transitions have been observed. Calculated phonon frequencies have been compared with available experimental data.

125 P 56 Tuesday, September 5

Inﬂuence of axial pressure on dielectric properties of AgNbO3 single crystals and ceramics J. Suchanicza, A. Kaniab, G. Stopaa and R. Bujakiewicz-Koro´nskaa aInstitute of Physics, Pedagogical Academy, ul. Podchor¸a˙zych 2, 30–084 Krakow, Poland bInstitute of Physics, University of Silesia, ul. Uniwersytecka 4, 40–007 Katowice, Poland

◦ The temperature dependence (30–550 C) of electric permittivities of AgNbO3 single crystals and ceramics under mechanical load (0–1 kbar) has been investigated. It was shown that axial pressure strongly changes the dielectric properties. This includes the shift of phase transitions temperature and the decrease of thermal hysteresis, which can be the evidence of changes of the transitions nature to that of the second order one. These eﬀects can be connected with change in domain structure, elastic change of distances between ions and change in defects density under the action of stress. The AgNbO3 is capable of sustaining large stresses without any mechanical degradati- on. The thermodynamic parameters of the phase transition were also determined and compared to that obtained by another method.

126 Tuesday, September 5 P 57

Phase transitions caused by the incommensurate phase existence

S. Sveleba, O. Semotyuk, I. Katerynchuk and I. Kunyo Ivan Franko National University of Lviv, Faculty of electronics, 107 Tarnavskogo Str., 79017 Lviv, Ukraine, E–mail: [email protected]

Existence of the incommensurate phase could be a reason of a sequence of phase transitions observed in the dielectric crystals. These transitions are: parent–incommensurate, commensurate–incommensurate–commensurate and transition between incommensurate phases. In the case of parent–incommensurate phase transition the coefficient α at the isotropic invariant of the thermodynamic potential expansion in this case is dependant on temperature. The temperature dependency of birefringence is characterized of a kink in the vicinity of this phase transition. The value of β (critical index, characterized temperature dependency of the order parameter amplitude) is good correlated with the theoretical value of 0.5, predicted by the Landau theory. The obtained value β differs from the values presented in earlier reports. The difference, to our mind, is caused by the contribution of correlated motion of tetrahedral groups (T-groups). The phase transition from one commensurate phase to another (in the incommensurate phase) passes through transition region – a region of coexistence of spatial modulation waves (a wave of defects modulation and wave of superstructure). As a result a modulation wave with a difference wave-vector (∆q = q1 − q2) appears. This one makes a main contribution to the anomaly temperature behavior of δ(∆ni). In other words in the incommensurate crystals a phase transition from one commensurate phase to another has a continuous character with corresponding behavior of physical parameters. That is why it is impossible to determine the type of phase transition between neighboring commensurate phases. A phase transition between two metastable states in the incommensurate phase passes through a transition region. The state of crystal is characterized by several modulation waves simultaneous existence. The resulted period of modulation wave can take an incommensurate value. It is confirmed by temperature behaviors of difference wave vector (∆q = q1 − q2), specific heat and birefringence.

127 P 58 Tuesday, September 5

Electron-phonon interaction in two well spherical nanoheterosystem HgS/CdS/HgS/CdS

M. Tkach and R. Fartushynskyi Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, 2 Kotsubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

General theory of electron-phonon interaction in closed complicated quantum dots is already established. The frequencies of confined and interface vibrations are obtained and their quantization is performed. The theory of electron spectrum renormalizati- on is developed in details only for the simplest closed quantum dots. The theory of electron-phonon interaction in opened quantum dots is absent at all because using the known quantum fields approaches it is impossible to make transition to representation of second quantization at the electron wave functions in opened system. This diffi- culty can be avoid observing the complicated nanosystem (well-barrier-well) placed into the external medium. The external well is to be so wide that the properties of closed system tendency to the respective opened one. The exactness of approximation is controlled by relationship between the semiwidths of respective quasistationary bands in closed and opened nanosystems. Analytical and computer calculations are performed for closed nanosystem HgS/CdS/HgS/CdS transiting into opened nanosystem HgS/CdS/HgS when the thickness of the second well limits to infinity. The phonon spectrum is obtained within dielectric continuum model. It is shown that the spectrum of closed system consists of two double degenerated modes of confined optical phonons and six modes of interface phonons degenerating into four when the thickness of the second well limits to infinity. All these modes have the weak dispersion over the thickness and orbital quantum number. Electron spectrum in closed spherical quantum dot is obtained within effective mass approximation and rectangular potential wells model. It is shown that for ∆ ≈ 3µm it corresponds to the quasistationary states of the respective opened spherical quantum dot. In the framework of Green functions method it is performed the calculation of renormalized energies of energy levels located near the resonance quasistationary states. There are calculated the partial contributions of all types of phonons into the shift of resonance level.

128 Tuesday, September 5 P 59

EPR and dielectric spectroscopy of the re-orienting 3+ + Cr –Li pair centers in Li2Ge7O15 crystals M.D. Volnianskii, M.P. Trubitsyn and Yahia A.H. Obaidat Department of the solid state physics, Dnipropetrovsk National University, vul. Naukova 13, Dnipropetrovsk 49050, Ukraine, E–mail: trub@ﬀ.dsu.dp.ua

3+ Earlier it has been shown that in the Li2Ge7O15 (LGO) structure Cr doping ions substitute for Ge4+ hosts and jointly with charge compensating interstitial lithium ions create Cr3+–Li+ paired centers [1,2]. The available experimental data allow to suppose that dipole moments of the Cr3+–Li+ pairs can re-orient under external electric ﬁeld eﬀect or as a result of temperature activation. Such re-orientations can be detected by means of the EPR and dielectric permittivity measurements. In this work we study EPR and dielectric spectra in LGO:Cr3+ crystals in the temperature range 300–500 K. In assumption that slight EPR line width broadening on heating results from the Cr3+–Li+ re-orientations, the activation energy has been estimated as U = 0.55(0.05) eV. Dielectric permittivity of LGO:Cr3+ has been measured in the frequency range 0.5–10 kHz. The typical for relaxation processes step-like anomalies of the real part 0(T ) and peaks of imaginary part ”(T ) were detected. The activation energy and mean lifetime determined from the dielectric data are U = 0.65(0.02) eV, −13 τ0 = 4(2) · 10 sec. Anisotropy as well as a good agreement of the radiospectroscopic data with dielectric ones unambiguously shows that EPR line width broadening and anomalies of ∗(ω, T ) arise from temperature activated re-orientations of the Cr3+–Li+ dipole moments. Reversing of the defects dipole moments may be realized by interstitial Li+ ions hopping through the structural channels of the LGO lattice. The experimental results show that structural distortions around Cr3+–Li+ paired defects may be considered as static in the frequency scale of the soft mode near ferroelectric phase transition in LGO crystals.

1. A.A. Galeev, et al., In: Spectroscopy, a crystal chemistry and real structure of min- erals and their analogs (Kazan’: Kazan’ univ., USSR, 1990) p. 77. 2. M.P. Trubitsyn, et al., Solid State Phys. (St. Petersburg), 2004, v. 46, N 9, p. 1676.

129 P 60 Tuesday, September 5

Nonlinear electrophysics properties of the crystals Bi12SiO20 doped by Al and Ga ions T. Panchenko and A. Urchik Dniepropetrovsk National University, 13 Naukova Str., 49050 Dniepropetrovsk, Ukraine, E–mail: [email protected]

Nonlinearity of electrophysics properties of photorefractive crystals of sillenite Bi12MO20 (where M = Si, Ge, Ti) is discussed in literature. It is known the hysteresis character of current-voltage (I–V) characteristics of sillenite, however the experimental data are insufficient, but the nature of the nonlinearity is not determine. It is found out with the barrier properties of contacts or with the hopping mechanism of conductivity.The results of complex research of I–V and farad-voltage (C–V) characteristics of crystals Bi12SiO20, undoped (BSO) and doped by Al and Ga ions (BSO:Al, BSO:Ga), are presented in this report. Crystals were grown by the Czochralski technique. The content of dopped ions in charge was ≈ 0,1 mass%. The influence on the features peculiar to I–V and C–V of formation photo-and thermoelectret state (PES and TES accordingly) in the research crystals was studied. Conditions of the formation PES and TES (polarizing voltage, temperature of polarization, wave-length of photoactivating illumination) were varied. As electrodes the platinum was used. Electrodes were obtained by the method of the cathode spraying in vacuum. The obtained results come to the following. Presence, formation and destruction PES and TES in the BSO, BSO:Al and BSO:Ga crystals play a determining role in the appearance (disappearance) of nonlinearity of I–U and C–V, type of their hysteresis, dependence of a degree of nonlinearity from cycling polarity and value voltage, the temperature of polarization, wave-length photoactivation in the visible range. The model describing nonlinearity I–U and C–V, used of diffusive theory of formation of Schottky barrier on Pt-BSO contacts and taked account of features of the PES and TES formation in undoped and doped BSO due to the mechanisms of volume- charge and guasidipolar polarization was proposed.

130 Tuesday, September 5 P 61

Conoscopic patterns for optically uniaxial gyrotropic crystals in the vicinity of isotropic point

Yu. Vasylkiv, Yu. Nastishin and R. Vlokh Institute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine, E–mail: [email protected]

We have presented computer simulations of conoscopic patterns occurring in optically uniaxial gyrotropic crystals in the vicinity of isotropic point for a number of sets of crystal parameters and orientations. The appearance of special directions characterized by equalization of linear and circular birefringences has been revealed. The conoscopic patterns calculated for gyrotropic crystals in the vicinity of their isotropic point display a number of distinctive features, which can be summarized as the appearance of special directions, where the total elliptical birefringence acquires extreme values and where the linear and circular birefringences are equal to each other. Those directions lie on the surface of cone, which can convolve into one axis parallel to z direction in optically uniaxial crystals with increasing linear birefringence or, alternatively, the angle of this cone can then approach some minimal value determined by the ratio of linear and circular birefringences. In the case of crystals belonging to the point symmetry group 42m , the surface of those directions is rather complicated and it reveals such the symmetry element as the four-fold axis, which coincides with z direction. Summing up the results of the present study, we have found a new peculiarity of the propagation of light in gyrotropic crystals characterized with commensurable values of the linear and circular birefringences: the appearance of special directions, for which the circular and linear birefringences become the same. Moreover, the above directions are characterized by a deﬁnite value of the eigenwave ellipticity, |k| = 0.414.

131 P 62 Tuesday, September 5

Domain structure in langbeinites. “Forbidden” domain walls

R. Vlokha, A. Saya, Ya. Buraka, O.V. Vlokha, I. Girnyka, Yu. Vasylkiva and Y. Uesub aInstitute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine, E–mail: [email protected] bWaseda University, Department of Physics, Tokyo, 169, Japan

The x, T -phase diagrams of Tl2xRb2(1−x)Cd2(SO4)3 and K2Cd2xMn2(1−x)(SO4)3 solid solutions is obtained and domain structure is studied. If to summarize the results of our present and recent study one can consider two diﬀerent scenarios of ferroelastic PT in langbeinites: 1. At the direct PT with change of symmetry 23F 222 domain structure most often appear in the view of heterophase structure, i.e. the sandwich like structure, which consists on the layers of ferroelastic domains and paraelastic phase. The two types of conjugated domain walls can appear at this process:

• pair of conjugated walls with {110}-orientation. The orientation of this walls coincide with the orientation of domain walls in other ferroelastic langbeinites and is explained on the base of remain walls, which exist between enantiomorphic twins, appeared due to the hypothetical PT with change of symmetry 43mF 23; • the type of domain walls which simultaneously play the role of phase boundaries. Pair of these conjugated walls with orientation, which deviate from 110-planes on some angle. The value of this angle depends on the orientation minimum of elastic energy of the phase boundary. These phase boundaries possess the same orientation as domain walls inclined to {110}-planes.

2. At the non-direct phase transition into ferroelastic phase (23F 2F 1F 222) the crystals usually are transformed into single domain state. The orientation of phase boundary is determined by the minimum of energy elastic non-compatibility between high-temperature phase and ferroelastic phase.

132 Tuesday, September 5 P 63

Properties of interface phonon spectra in complicated cylindrical nanosystem

O. Voitsekhivska and A. Gryschyk Yurii Fed’kovych National University of Chernivtsi, Faculty of physics, 2 Kotsubynsky Str., 58012 Chernivtsi, Ukraine, E–mail: [email protected]

The experimental treatment of the quantum objects exhibiting the variety of shapes such as sphere, cylinder or rectangle, have brought to the creation of rather complicated combined constructions with dimensions in a range of few nanometers. Nanoconstructi- ons can contain different spatial combinations of quantum dots, wires and wells and are actively studied in spite of the mathematical difficulties arising due to the complicated fitting conditions for the wave functions of quasiparticles and polarization potentials of phonons. Obviously, it is necessary to perform precise description of all optical phonon modes in the combined nanosystem. The energy spectra of interface phonons are studied for the two types of combined nanoheterosystem consisting of cylindrical quantum dot embedded inside of cylindrical quantum wire placed into semiconductor or dielectric external medium. The phonon spectra are treated within the dielectric continuum model widely applied for the investigation of low-dimensional crystal structures and the results of which are correlating to experimental data. The height of quantum dot and radius of quantum wire, the dielectric constants and frequencies of LO and TO vibrations for the bulk analogies of all parts of nanosystem are assumed as known. From the solution of electrostatic equations it is established that there are two types of surface modes called as top surface optical (TSO) and side surface optical (SSO) modes which is different from other quantum structures where only one kind of side phonon modes exist. From the boundary conditions at side interfaces the transcendental equation for the defining of SSO phonons spectrum is obtained. The fitting conditions for top interfaces give the system of equations for the symmetric and anti symmetric frequencies of TSO phonons. The dependences of both types of phonon frequencies on the respective quantum wave numbers are calculated for different parameters of quantum dot height and quantum wire radius.

133 P 64 Tuesday, September 5

Temperature and pressure eﬀects on lattice dynamics of Sn2P2S6 monoclinic ferroelectrics R. Yevych and Yu.M. Vysochanskii Institute for Solid State Physics and Chemistry, Uzhgorod National University, 54 Voloshyna Str., 88000 Uzhgorod, Ukraine, E–mail: [email protected]

A previously used model [1] of the lattice dynamics of the Sn2P2S6 monoclinic proper ferroelectrics was applied for the analysis of a diﬀerent inﬂuence of a temperature and pressure on the phase transition of the investigated crystals. A lattice dynamics calculations within the framework of a polarizable ion model were performed. An instability of the lowest frequency polar optical BU mode of a paraelectric phase P 21/c and a form of dispersion branches of soft optic phonons were observed as a function of the lattice volume. A linear interaction of a polar optical BU mode with a full symmetry lowest optical Ag modes was found. This interaction according to the lattice parameters changes governs on the form of a dispersion curves of the lowest optical phonons and, as a result, on the temperature of phase transition. The role of short range and dipole-dipole interaction on these occurring was analyzed by calculating a changes of the Madelung constant of a structure.

1. R.M. Yevych, Yu.M. Vysochanskii. Lattice dynamics and phase transitions in Sn2P2S(Se)6 ferroelectric crystals. // Condens. Matter Phys. (in press).

134 Tuesday, September 5 P 65

Phase transitions and phase separations in an S = 1/2 pseudospin-electron model and ferroelectricity in intercalated compounds

Yu.I. Dublenych Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine

An electron-ion lattice gas model is used to describe phase transformations in intercalated layered crystals. The model can be reduced to an S = 1/2 pseudospin-electron model without electron transfer. We have considered several types of lattices on the base of triangular one for ion (pseudospin) sublattice: 1) the lattice in which each electron site is attached to one and only one ion site, 2) the lattice in which in addition to the sites of the first type there are also isolated electron sites, 3) the lattice in which each electron site is attached to two ion sites. It is shown that the partition function of the model can be presented as a product of the Ising model partition function with shifted parameters and of the partition function of electron subsystem. The shifts depend on temperature and on the parameters connected with electrons. For lattice 1 and 2 only chemical potential of ions (external field) is shifted and for lattice 3 the interaction perpendicular to layers is also shifted. First order phase transitions and phase separation to the phases with different electron and ion concentrations are possible in the model. Different kinds of phase separation are considered: separation at fixed chemical potential of ions and fixed electron concentration, separation at fixed both ion and electron concentrations (double separation), separation at fixed neutral particle concentration. For lattices 1 and 2 the separation curbs can be calculated exactly; for lattice 3 mean field approximation is used. It is shown that in the case when the electroneutrality condition is satisfied for the crystal in general this condition is not satisfied for each separated phase therefor charged domains can appear in the intercalated crystal that leads to the electrical polarization.

135 P 66 Tuesday, September 5

Inﬂuence of σ1 − σ2 stress on transverse relaxation dynamics in the KD2PO4 type ferroelectrics R.R. Levitskiia, I.R. Zachekb and A.S. Dudaa aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bLviv Polytechnical National University, 12 Bandera Str., 79013 Lviv, Ukraine

In the present work within a previously proposed model [1] of a crystal deformed by the σ1 −σ2 stress and the Glauber kinetic approach we study the inﬂuence of this stress on the transverse relaxation dynamics in the KD2PO4 type crystals. In the approximation of small deviations from equilibrium, we ﬁnd expressions for the transverse dynamic dielectric permittivities ε1(ν, T ) and ε2(ν, T ), as well as the corresponding relaxation times. Their frequency, temperature, and stress dependences are explored. It is shown that the permittivities and the relaxation times have peculiarities at the phase transitions, especially at transition into the stress induced monoclinic phase. Discontinuous changes of the dispersion frequencies at this transition are detected.

1. I.V. Stasyuk, R.R. Levitskii, I.R. Zachek, A.S. Duda // Condens. Matter Phys, 2001, vol. 4, No 3(27), p. 553–578.

136 Tuesday, September 5 P 67

Inﬂuence of temperature on the piezo-optic eﬀect in LiNbO3:MgO crystals B. Mytsyk, A. Andrushchak, H. Haskevych and I. Solskii Lviv Center Institute Space Research, 5a Naukova Str., 79000 Lviv–60, Ukraine, E–mail: [email protected]

Crystals of lithium niobate, alloyed by magnesium (7% MgO in the melt), were grown by the Czochralski technique and poled at the temperature T = 1200◦C. The slow lowering of temperature from Tpoling to the room temperature provided minimization of internal tensions in specimens and their high optical quality. Specimens for researches with dimensions ≈ 8×8×8 mm were cut from central part of crystalline boules with dimensions of 84×60 mm. Pure lithium niobate is widely used in electro- and acoustooptic. An important advantage of the LiNbO3:MgO crystal as compared to the pure crystal is their in 2–3 times higher radiation firmness. However for these crystals there are not studied those optical parameters on the basis of which it is possible to set efficiency of application of the optical material in electro- and acoustooptic devices. In this work for the crystals alloyed by magnesium the complete study of piezoelectric effect has been conducted: certain piezo- optic coefficients (POCs) of birefringence, retardation and absolute POCs are determined. On the basis of results of these researches the piezo-optic (see Fig. 1) and elasto-optic surfaces have been built, analysis of which allowed to determine crystal physic directions of specimens with the optimized acoustooptical descriptions. The temperature stability is the important parameter of acoustooptical cells. Influ- ence of temperature is therefore examined on piezo- and elasto-optical coefficients, and also studied the temperature dependence of the crystals LiNbO3:MgO birefringence in the temperature interval 20 ÷ 120◦C. These results are compared to similar for the pure crystals of lithium niobate and tantalate. New aspects of method of the precise de- Figure 1: An example of piezo-optical surface termination of absolute POCs of crystals are of mechanical stress for the direction of vibra- discussed also. The use of this method al- tions of a light wave electrical vector i(θ,ϕ)= lows to eliminate large errors of the POCs i(54◦, 90◦); θ,ϕ – spherical co-ordinates. determination, related to typical unparallel of faces of specimens with value 0.02 deg.

137 P 68 Tuesday, September 5

Thermodynamics and relaxational dynamics of the KH2PO4 type ferroelectric compounds: a uniﬁed model R.R. Levitskiia, I.R. Zachekb and A.S. Vdovycha aInstitute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine, E–mail: [email protected] bLviv Polytechnical National University, 12 Bandera Str., 79013 Lviv, Ukraine

The aim of the present study is to explore the dielectric dispersion and thermody- namical properties of the ferroelectric the crystals of the KH2PO4 family. The physical characteristics of these crystals are calculated within the unified proton ordering model in the four-particle cluster approximation with taking into account short-range config- urational correlations of protons (deuterons) as well as long-range interactions between them. The temperature dependences of the static dielectric permittivity tensor, spontaneous polarization, relaxation times, and specific heat, as well as the frequency and temperature dependences of the longitudinal and transverse dynamic dielectric permittivities are calculated. The calculations for the partially deuterated compounds are performed within the mean crystal approximation, and the model parameters are taken to be linear functions of deuteration. It is shown that at the proper choice of the theory parameters a good quantitative description of experimental data for pure and partially deuterated ferroelectric crystals of the KH2PO4 family is obtained. Our results confirm validity of the proton ordering model for these compounds.

138 Tuesday, September 5 P 69

Ferroelectric phase transition in (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 crystals R. Poprawski, A. Ci˙zman and A. Sieradzki Institute of Physics, Wroclaw University of Technology, Wybrze˙ze Wyspia´nskiego 27, 50–370 Wroclaw, Poland, E–mail: [email protected]

(CH3NH3)5Bi2Cl11 (MAPCB) and (CH3NH3)5Bi2Br11 (MAPBB) are members of the subfamily of alkylammonium halogenobismuthes (III) crystals showing an interesting ferroelectric properties. At 307 K (312 K) MAPCB (MAPBB) undergoes a ferroelectric phase transition from the phase mmm (space group P cab) to the ferroelectric mm2 phase (space group Pca21) [1,2]. Temperature dependence of the linear birefringence ∆n and excess entropy ∆S in a phase transitions regions for the (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 ferroelectric crystals will be discussed. We conﬁrmed the linear relation between ∆n and ∆S in the temperature range from 285 to 306 K and from 295 to 306 K for (CH3NH3)5Bi2Cl11 and (CH3NH3)5Bi2Br11 crystals respectively.

1. R. Jakubas, L. Sobczyk, J. Lefebvre, “A new ferroelectric crystal: (CH3NH3)5Bi2Cl1”, Ferroelectrics, 100 143 (1989). 2. M. Iwata, Y. Ishibashi, “On an isomorphous transition”, J. Phys. Soc. Jpn., 60, 1634 (1991). 3. B. Mroz, J.A. Tuszynski, R. Jakubas, D. Sept, H. Kiefte and M.J. Clouter, “Brillouin- scattering studies of ferroelectric (CH3NH3)5Bi2Cl11”, Phys. Rev. B, 58 261 (1998). 4. B.A. Strukov, R. Poprawski, S.A. Taraskin, J. Mróz, “Specific heat of (CH3NH3)5Bi2Cl1 crystals: evidence of overcritical behavior”, Phys. Stat. Sol., 143, K9 (1994). 5. A. Pawlowski, R. Jakubas, S. Ramos and J. Del Cerro, “Specific heat behavior of (CH3NH3)5Bi2Br1 near its ferroelectric transition”, Ferroelectrics, 125, 29 (1992).

139 P 70 Tuesday, September 5

Phase transitions in (TEA)2MnCl4 crystals A. Ci˙zmana, R. Poprawskia, D. W losewiczb and A. Sieradzkia aInstitute of Physics, Wroclaw University of Technology, Wybrze˙ze Wyspia´nskiego 27, 50–370 Wroclaw, Poland, E–mail: [email protected] bInstitute of Low Temperature and Structure Reserch, Polish Academy of Sciences, P.O. Box 937, 50–950 Wroclaw 2, Poland

[N(C2H5)4]2MnCl4 crystals (abbreviated hereafter as (TEA)2MnCl4) belong to a + + widely studying family with general formula A2BX4,withA = Cs,Rb,Et4N , ME4N , B = Cu, Mn, Fe, Co, Ni, Zn, and X = Cl, Br, F, which exhibit many interesting physical properties. The calorimetric properties of (TEA)2MnCl4 in a wide temperature range will be presented. Two anomalies typical for the ﬁrst order phase transition at T1 = 224 K and T2 = 231 K with entropy jumps of 15 J/molK and 12 J/molK were observed.

Figure 1: Phase diagram of (TEA)2MnCl4 crystals.

The dielectric measurements conﬁrmed the typical anomaly for the ﬁrst order phase transition in temperature T1 = 231 K and T2 = 224 K. The big temperature hysteresis for low phase transition is observed. From the dilatometric measurements the big deformation near the phase transitions in all crystallographic directions was observed.

1. O. Caetano, M. Lopez, A. Mahoui, J. Lapasset, J. Moret, T. Assih and P. Saint- Gregoire, Ferroelectrics Letters, 19, 69, (1995). 2. M. Kahrizi and O. Steinitz, Solid State Comm., 74, 333, (1990). 3. Z. Tylczy´nski, P. Biskupski and M. S laboszewska, Ferroelectrics, 272, 315, (2002). 4. A.D. W losewicz, T. Plackowski and K. Rogacki ,Cryogenics, 32, 3, (1992). 5. R. Poprawski, M. Drulis and A. Liber, Ferroelectics Lett., 27, 91, (2000).

140 Tuesday, September 5 P 71

Dielectric properties and phase transitions of KNO3 embedded into porous glasses E. Rysiakiewicz-Pasek, R. Poprawski, A. Sieradzki and J. Polanska Institute of Physics, Wroclaw University of Technology, Wybrze˙ze Wyspiańskiego 27, 50–370 Wroclaw, Poland Thin ferroelectric films and low-size ferroelectric matrices are applied in such devices, so the size-effect investigation is crucial, particularly with respect to physical properties and phase transitions. Nanosized ferroelectrics are promising for their potential application in ferroelectric memories. One of the candidates is potassium nitrate (KNO3) [1–3]. The size effect is also a main problem in fundamental physics. Introducing ferroelectric materials into a porous glass matrix is one of the methods of preparating nano-size ferroelectrics, but publications on porous glasses filled with a ferroelectric are few (see e.g. [4,5]). Introducing of KNO3 into the porous glasses allows to build a physical system for ferroelectric properties investigation at the nano-size scale. KNO3 monocrystals (bulk material) exhibit only one phase transition at about T = 130◦C when heating and ◦ ◦ two transitions (about T1 = 124 C and T2 = 108 C) when cooling. In the temperature range from 108◦C to 124◦C the crystal is in the ferrrolectric phase [6]. The dielectric measurements of porous glasses filled with KNO3 will be presented. Porous glasses were fabricated by etching off the sodium borate phase from two- phase sodium borosilicate glasses. Two types of porous glasses with different pores sizes (45 nm and 320 nm) were used. The ferroelectric was introduced from water solutions or from melted KNO3. The measurements were performed in the temperature range from 70◦C to 170◦C. The observed anomalies of dielectric permittivity are connected with phase transitions in KNO3 nanocrystals. These transitions are similar to those of the bulk material, but happen at lower temperatures. Thermal hysteresis, similar to the thermal hysteresis of bulk monocrystals was registered. The observed peculiarities of KNO3 in microvoids are attributed to size effects.

1. C. Araujo, J.F. Scott, R. Bruce Godfrey, L. McMillan: Applied Physics Letters, 48, (1986) 1439–1440. 2. K. Dimmler, M. Parris, D. Butler, S. Eaton, B. Pouligny, J.F. Scott, Y. Ishibashi: J. Appl. Phys., 61, (1987) 5467–5470. 3. J. Kim, L. Kim, D. Jung, Y,S. Kim, J.W. Kim, J.H. Je, J. Lee: Jpn. J. Appl.Phys., 43, (2003) 5901–5903. 4. E.V. Colla, A.V. Fokin, Yu.A. Kumzerov, Solid State Comm., 103, (1997) 127. 5. A. Nabereznov, A. Fokin, Yu. Kumzerov, A. Sobotnikov, S. Vakhrushev, B. Dorner, Eur. Phys. J. E, 12, (2003) S21. 6. A. Mansingh, A.M. Smith: J. Phys. D: Appl. Phys., 4, 1971, 560–567.

141 P 72 Tuesday, September 5

Phase situation in cyanopiridinium perchlorate crystals [CNC5H4NH][ClO4] O. Czupi´nskia, M. Wojta´sa, A. Pietraszkob and R. Jakubasa aFaculty of Chemistry, University of Wroclaw, 50–383 Wroclaw , Poland, E–mail: [email protected] bInstitute of Low Temperature and Structure Research of the Polish Academy of Science, 50–950 Wroclaw, Poland

In the last years, much attention has been devoted to simple complex organic- inorganic systems due to their interesting non-linear physical properties. The het- − − − − eroatomic pyridine cations with BF4 , ClO4 , IO4 and FCrO3 anions form a large group of molecular ionic crystals showing ferroelectric properties [1–3]. In all types these crystals not only the heteroatomic cations are disordered revealing rapid reorientation within the aromating ring but also the degeneration the vibration modes of the anion molecules are observed. Our early studies on simple ionic salts with substituted pyridinium cation with tetraﬂuoroborate and perchlorate cation e.g. [4-NH2C5H5N][ClO4] and [BF4] disclosed the phase situation and properties of these systems [4–5]. Now we would like to present the phase situation in cyanopyridinium perchlorate derivatives. The diﬀerential scanning calorimetry, FT-IR spectroscopy, dilatometry, pyroelectric and dielectric spectroscopy have been used to study of these salts. The properties of 2-cyanopyridinium, 3-cyanopyridinium and 4-cyanopyridinium perchlorate will be presented in our presentation [6-7]. Now we would like to present the phase situation in cyanopyridinium perchlorate derivatives.

1. Z. Paj¸ak, P. Czarnecki, J. W¸asik, W. Nawrocik, J. Chem. Phys. 109 6420 (1998). 2. Z. Paj¸ak, P. Czarnecki, H. Muszyńska, B. Szafrańska, J.Chem. Phys. 113 848 (2000). 3. Z. Paj¸ak, H. Muszyńska, B. Szafrańska, P. Czarnecki, J.Chem. Phys. 117 5303 (2000). 4. O. Czupiński, G. Bator, Z. Ciunik, R. Jakubas, W. Medycki and J. Swiergiel,´ J. Phys.: Condens. Matter 14 8497 (2002). 5. O. Czupiński, R. Jakubas, A. Pietraszko, J. Mol. Struct. 704 177 (2004). 6. O. Czupiński, M. Wojta´s,J. Zaleski, R. Jakubas and W. Medycki J. Phys. Condens. Matter 18 1 (2006). 7. O. Czupiński, M. Wojta´s,R. Jakubas, A. Pietraszko, J. Mol. Struct. (submitted).

142 Tuesday, September 5 P 73

Electromechanical properties of crystals in system Li2Ge4O9–LiNaGe4O9 O.Yu. Shulichenko Dnipropetrovsk National University, 13 Naukova Str., 49050 Dnipropetrovsk, Ukraine, E–mail: [email protected]

Abstract was not available at printing time.

143

Index Adamiv V., 54 Eliyashevskyy Yu., 25, 78, 82 Agarkov K., 112 Ermakov A.S., 80 Andriyevsky B., 71, 72 Esser N., 71 Andrushchak A., 137 Andrusyk A.Ya., 73, 74 Fartushynskyi R., 128 Franiv A.V., 121 Bak Z., 48 Baran O.R., 97 Galdina A., 116 Baysa N.D., 43 Garbarz-Glos B., 83, 91, 115 Beley L., 24, 99 Gaza L.S., 76 Belous A.S., 80 Gaza Yu.Yu., 76, 108 Benet S., 103 Gerzanich E.I., 32 Bercha D.M., 75, 113 Girnyk I., 132 Biedrzycki K., 50 Glinchuk M.D., 26, 81 Bilanych V.S., 43, 110 Gomonnai A.V., 84 Bodnar K.V., 76 Gomonnai O.O., 57 Bovgyra O.V., 121 Grabar A.A., 27, 76 Bujakiewicz-Korońska R., 126 Grabovsky S., 40 Burak Ya., 54, 132 Grigas J., 23 Grygorchak I.I., 29 Chobal O.I., 111 Gryschyk A., 100, 133 Chyzh O.Z., 119, 121 Guranich P.P., 32, 57 Cicha M., 50 Gurzan M., 27, 99, 108 Ciepluch-Trojanek W., 71, 72 Gutsul V., 86 Ci˙zman A., 139, 140 Guyvan H.M., 88 Cobet C., 71 Czapla Z., 25, 33, 38, 78, 82, 85, 93 Haskevych H., 137 Czupiński O., 142 Hasynets’ S., 107 Hek A., 33, 85 Cwikiel´ K., 30, 77 Holovatsky V., 86 Holovey V.M., 43 Dacko S., 25, 33, 78, 85, 93 Horvat A., 27 Dambekalne M., 83, 115 Hrabański R., 38 Dan’kiv O., 104 Danko M.M., 76, 108 Jakubas R., 142 Dec J., 28, 30 Janiec-Mateja M., 38 Dovganiuk M., 100 Dublenych Yu.I., 135 Kania A., 126 Duda A.S., 136 Kapustyanyk V.B., 58 Duda V.M., 79, 80, 94 Katerynchuk I., 87, 127 Dyachok Ya., 53 Kaynts D., 27 Kedyk I.V., 76 Eliseev E.A., 26, 49, 81 Kedyulich V.M., 74, 88, 114

145 Kharchenko M., 51, 90 Matyjasek K., 55, 101 Kharchenko Yu., 89 Menchyshyn O., 29 Kharkhalis L.Yu., 75 Michel D., 34 Khoma M., 24 Miga S., 30 Khrustalyov V., 90 Moina A.P., 52, 74 Kityk I.V., 45, 103 Morozovska A.N., 26, 49, 81 Kleemann W., 28 Motrya S., 107 Knorr K., 31 Mykailo O., 107 Konieczna B., 50 Mys O., 46, 54 Konieczny K., 91 Mytsyk B., 137 Konstantinovich A.V., 92 Konstantinovich I.A., 92 Nastishin Yu., 131 Korda N., 99 Nogas-Cwikiel´ E., 77, 102 Korynevskii N.A., 47, 96 Nouneh K., 103 Kosturek B., 25, 93 Obaidat Yahia A.H., 129 Kozlovskii M., 42 Odrekhivs’ka O., 104 Kranjˇcec M., 124 Olszowy M., 102 Krokhmal’ Yu.D., 39 Ozga K., 45, 103 Krupych O., 53, 54 Kruzina T.V., 79, 94 Panchenko T., 123, 130 Ku lek J., 102 Pankivskyi Yu., 87 Kunyo I., 87, 127 Patryn A., 71, 72 Kuriata J., 96 Pawlaczyk Cz., 102 Kuritsa I.Yu., 57 Peleshchak R., 104, 105 Kushnir O.S., 95 Piasecki M., 45 Ku´sCz., 91, 115 Pietraszko A., 37, 142 Kutny I.V., 73 Polanska J., 141 Kuzyk O., 105 Polovynko I., 106 Lazauskas V., 23 Popov S.A., 94 Levitskii R.R., 41, 52, 73, 74, 97, 117, 136, Poprawski R., 82, 139–141 138 Potorii M., 107 Linnik V.G., 80 Pozdeev V.G., 94 Lipi´nski I.E., 96 Prits I.P., 32, 98, 107, 108 Lisnii B.M., 97 Pylyuk I.V., 109

Lukasiewicz T., 28 Remiens D., 49 Lukaszewicz K., 37 Rizak I.M., 43, 110, 111 Rizak V.M., 43, 110, 111 Maior M.M., 98, 99 Roginskii E.M., 31 Makauz I.I., 98 Rogowski R.Z., 55, 101 Makhanets O., 100 Romanyuk M.M., 71, 118 Markiewicz E., 102 Romanyuk M.O., 119, 120 Markov Yu.F., 31 Rud’ko M., 35 Martynyuk-Lototska I., 54 Rudyk V.P., 58

146 Rushchanskii K., 125 Sveleba S., 87, 127 Rykhlyuk S., 106 Swartsman V.V., 28 Rysiakiewicz-Pasek E., 141 Sznajder M., 75

Sadovskaya L., 112 Smiga´ W., 83, 91, 115 Savitsky V., 90 Talik E., 23 Say A., 132 Tkach M., 35, 128 Schranz W., 54 Tovt V., 107 Semotyuk O., 87, 127 Trubitsyn M.P., 39, 129 Seti Ju., 35 Trybula Z., 41, 43 Shchur Ya., 36 Tuzyak M.R., 120, 121 Shnaidshtein I., 40 Shopa R.Y., 95 Uesu Y., 132 Shtym V., 105 Urchik A., 130 Shulichenko O.Yu., 143 Shusta V.S., 32 Vachulovych V.F., 119 Sieradzki A., 82, 139–141 Vasylkiv Yu., 131, 132 Sitko D., 83 Vdovych A.S., 41, 52, 117, 138 Sko lyszewski D., 83 Velychko O.V., 29 Slezak A., 103 Vlokh O., 54 Slipukhina I.V., 75, 113 Vlokh O.V., 132 Slivka A.G., 57, 74, 88, 114 Vlokh R., 46, 53, 54, 131, 132 Smaga I., 53 Voitovych S., 29 Soldatova E.D., 116 Voitsekhivska O., 133 Solovyan V.B., 47 Volnianskii M.D., 129 Solskii I., 137 Vorobyov O., 56 Sorokov S.I., 41, 117 Vysochanskii Yu.M., 24, 76, 98, 99, 134 Soyer C., 49 Waplak S., 39 Stadnyk V.Yo., 118–121 Wa´skowska A., 93 Stankowska J., 118 W losewicz D., 140 Stankowski J., 44 Wojta´sM., 142 Stasyuk I.V., 29, 56, 122 Stenberg A., 115 Yevych R., 134 Stephanovich V., 125 Sternberg A., 83 Zachek I.R., 52, 73, 74, 136, 138 Stetsiv R., 122 Stoika I., 108 Stopa G., 91, 115, 126 Strelets K., 123 Strukov B., 40 Studenyak I., 124, 125 Studenyak I.P., 57 Suchanicz J., 83, 115, 126 Susla A.I., 114

147

VIII Ukrainian-Polish and III East-European Meeting

on Ferroelectrics Physics

Notes

4–7 September 2006, Lviv, Ukraine

VIII Українсько-Польська та III Схiдно-Європейська конференцiя з фiзики сегнетоелектрикiв Львiв, 4–7 вересня 2006 р.

Програма i тези доповiдей

c Iнститут фiзики конденсованих систем НАН України Львiв, 2006

Комп’ютерне макетування: Андрiй Швайка, Олег Величко

Укладання: Олег Величко