Normal Vibrations of Two Polymorphic Forms of Teo2 Crystals and Assignments of Raman Peaks of Pure Teo2 Glass

Nippon Seramikkusu Kyokai GakujutsuRonbunshi 97 [12] 1435-40 (1989) 1435 Normal Vibrations of Two Polymorphic forms of TeO2 Crystals and Assignments of Raman Peaks of Pure TeO2 Glass Takao SEKIYA, Norio MOCHIDA, Atsushi OHTSUKA and Mamoru TONOKAWA† ( Division of Materials Science and Chemical Engineering, Faculty of Engineering, Yokohama National University, 156, Tokiwadai, Hodogaya-ku, Yokohama-shi 240) TeO2結晶の二つの多形の基準振動の計算とTeO2ガラスのラマンピークの帰属関谷隆夫・持田統雄・大塚淳・殿川衛 † (横浜国立大学工学部物質工学科, 240横浜市保土ケ谷区常盤台156) Raman spectra of paratellurite, tellurite and pure TeO2 glass were measured. The normal vibration of paratellurite and tellurite was analyzed. The spectrum of pure TeO2glass were deconvoluted into symmetric Gaussian functions. The normal vibrations of paratellurite are exactly described as combined representations of movement of oxygen atom in Te-eqOax-Te linkage and vibrations of TeO4 trigonal bipyramid (tbp). Compared the resolved Raman peaks of pure TeO2glass with nor mal vibration of paratellurite, all Raman peaks from 420 to 880 cm-1 are assigned to the vibrations of TeO4 tbp and Te-eqOax-Te linkage. The antisymmetric stretching vibrations of Te-qeOax-Te linkage have relatively large intensities to symmetric stretching vibrations of Te-eqOax-Te linkage. In pure TeO2 glass, TeO4 tops are formed by most of tellurium atoms and connected at vertices by the Te-eqOax-Te linkages. [ReceivedMay 18, 1989; AcceptedAugust 22, 1989] Key-words: Normal vibration, Raman spectrum, Paratellurite, Tellurite, Pure TeO2glass 1. Introduction network modifiers, were added to TeO2. But pure Tellurium dioxide is one of the typical glass TeO2 glass structure was not investigated. Re forming oxides. The TeO2-based glasses have cently, it was reported that tellurium dioxide wide glass forming range and several useful itself became glassy state when a small batch of properties such as low melting temperature, high its melt was cooled rapidly.7) refractive index and good transmittance of infra Vibrational spectroscopy is one of the most red.1)-5) powerful techniques for studying the structure of The coordination states of TeO3 Te4+ ions are glass. For the purpose of analysis of the structure TeO4 trigonal bipyramid (tbp), trigonal pyramid of pure TeO2 glass, Raman spectra of two and these intermediate states in crystals contain polymorphic forms of crystalline TeO2 (para ing TeO2. The structure of TeO4 tbp is described tellurite and tellurite) were investigated. Raman as that one equatorial site of the Te sp3d hybrid spectrum of pure TeO2 glass was measured and orbitals is occupied by a lone pair of electrons and deconvoluted into the symmetric Gaussian func the other two equatorial and two axial sites are tions. The resolved Raman peaks were investi occupied by oxygen atoms. In the TeO3 trigonal gated with the results of normal vibration ana pyramid, one of the Te sp3 hybrid orbitals is lysis. occupied by a lone pair of electrons. For the structure of TeO2-based glasses, 2. Experimental procedure Mochida et al.6) concluded from study of IR 2.1 Preparation of specimens spectra that the coordination states of part of Te Tellurite (ƒÀ-TeO2) was used as raw materials . atoms changes from TeO4 tbps to TeO3 pyramids Paratellurite (ƒ¿-TeO2) was prepared by melting when mono- and di-valent cations, that is typical of TeO2 and then crystallizing. Pure TeO2 glass was prepared by melting of 0.1-0 .2g TeO2 batch †Now Foundation for Promotion of Material Science and in Pt crucible and then cooling by dipping Technology of Japan, 3-11-1, Kamisoshigaya, Setagaya crucible bottom into ice-cold water ku, Tokyo 157 . The speci 現在: (財) 材料科学技術振興財団, 157東京都世田谷区上 men was confirmed to be glassy state by X-ray 祖師谷3-11-1 diffraction pattern and DTA analysis . Normal Vibrations of Two Polymorphic Forms of TeO2 Crystals and 1436 Assignments of Raman Peaks of Pure TeO2 Glass 2.2 Measurement of Raman spectra tellurite. Raman spectra were measured in the wavenum The program of optimization was made for NEC ber range from 20 to 1200 cm-1 using Ar+ laser PC-9801 series computer in our laboratory . (514.5nm, 200mW) and R-800 laser Raman spectrophotometer with third monochrometer sup 3. Results and discussion plied by Japan Spectroscopic Co., Ltd. 3.1 Paratellurite, ƒ¿-TeO2 Raman spectrum of paratellurite is shown in (JASCO). For pure TeO2 glass, polarized spec tra, I•V and I•Û, were measured and depolarization Fig. 1. ratio, ƒÏ, was determine as following equation. The crystal data of paratellurite have been given by Lindgvist10): tetragonal, P41212-D44, a where I•V and I•Û are the intensities of scattered lights, when polarization vector of scattered beam are parallel and perpendicular to that of incident beam, respectively. The spectrum was separated in the wavenumber range from 420 to 880cm-1 by a curve fitting method using the symmetric Gaus sian function as a profile function. Peak posi tions, intensities, half widths and depolarization ratios were optimized. 2.3 Analysis of normal vibrations The analysis of normal vibration was carried out with the mass corrected Cartesian symmetric displacement coordinate method. Simple Urey- Bradley force field was used as internal potential field. For paratellurite, Raman peaks had be already assigned by Pine et al.8) The force constants of stretching of valence bonds, K, bending of bonds, H, and repulsion between nonbonded atoms, F, were set as Table 1 and optimized by the brute force method. The initial values of force constants of stretching for the optimization were estimated from that of TeO32- ion,9) and the other force constants were assumed to be zero. No reports for assignment of Raman peaks of tellur ite, exists. Using optimized force constants, Fig. 1. Raman spectra of two polymorphic forms of normal vibrations were tentatively calculated for TeO2 crystals, paratellurite and tellurite. Table 1. Force constants and calculated and observed frequencies of paratellurite. T. SEKIYA et al. 1437 A1 species (Vs1TeO4, VasTe-eqOax-Te) A1 species (δs1TeO4, VsTe-eqOax-Te) Vcalc.=668cm-1 Vcalc.=449cm-1 Vobs Vobs.=649cm-1 .=392cm-1 B1 species (VasTeO4, VasTe-eqOax-Te) B2 species (δs2TeO4, VsTe-eqOax-Te Vcalc.=645cm-1 ) Vcalc .=440cm-1 Vobs.=589cm-1 Vobs .=415cm-1 Fig. 2. Normal vibrations of paratellurite. The compo B2 species (Vs2TeO4, VasTe-eqOax-Te) nents of atomic displacement vector are indicated by Vcalc.=750cm-1 x, y and z. Vobs.=786cm-1 to electrostatic interactions. The optimization of =4 .812•ð, c=7.615•ð and z=4. The structure of paratellurite is a three-dimensional network force constants was carried out for A1, B1 and B2 built up from the TeO4 tbp, sharing vertices and species to disregard LO-TO split. containing only Te-eqOax-Te linkages. The force constants and calculated frequency The Bravais cell of paratellurite contains four values are listed in Table 1. The agreement TeO2 units resulting in 36 phonon branches with between the calculated and observed values is ƒ¡= 4A1+5A2+5B1+4B2+9E. Of these 1A2+ reasonably good. If Coulonb interaction is consi 1E comprise the acoustic modes. A1, B1, B2 and dered as a long range force, the difference E species are Raman active. A2 and E species between observed and calculated frequency which are infra-red active are split to longitudinal values will be smaller. But simple Urey-Bradley (LO) and transverse (TO) optical modes owing force field is sufficient for our purpose of analysis Normal Vibrations of Two Polymorphic Forms of TeO A 2 Crystals and 1438 ssignments of Raman Peaks of Pure TeO 2 Glass of vibrational types of TeO4 tbp and its applica Table 2. Calculated and observed frequencies of tel tion for pure TeO2 glass. lurite. The vibrational modes for paratellurite , which have relatively large frequencies, are shown in Fig. 2. These modes are exactly described as combined representations of the vibrations of TeO4 tbp and the movement of bridging oxygen atom in Te-eqOaX-Te linkages. In A1 species at 668cm-1, two equatorial bonds stretch in the same phase, two axial bonds in the same phase and two types of bonds in the reverse phase. This mode is assigned to vs1 TeO4 from the atomic displacement of TeO4 tbp. In B1 species at 645cm-1, two equatorial bonds stretch in the reverse phase and two axial bonds vibrate in the same manner. It is assigned to vas TeO4. The B2 species at 750cm-1 is assigned to vs2TeO4 , where all the Te-O bonds of each TeO4 tbp stretch in the same phase. The modes at 696cm-1 and 653cm-1 belong to E species. The former mode contains two types of atomic displacement of TeO4 tbp . tentatively appropriated for those of tellurite . One is regarded as atomic displacement of TeO4 The observed and calculated frequencies of Ra tbp in vs2 TeO4 and the other is in vas TeO4 . In the man active modes are listed in Table 2. case of the latter mode, one is in vs1 TeO4 and the The symmetry assignment of observed Raman other is in VasTeO4 (The schemes of these modes peaks is not clear. The suitability of appropria are omitted). Therefore, they are assigned to tion of the force constants of paratellurite is vs2+asTeO4 and vs1+asTeO4, respectively. These doubtful because tellurite contains Te2O2 four- five vibrational modes are assigned to antisym membered ring due to edge sharing of TeO4 tpbs . metric vibrations of Te-eqOax-Te linkage .

Load more