Z. Kristallogr. NCS 215 (2000) 465^66 465 © by Oldenbourg Wissenschaftsverlag, München

Crystal structure of barium bismuth , Ba(Pbo.9Bio.i)03

O. Moretzki*1, T. Doering1, M. Steins1, M. Wendschuh-Josties11 and K. Bente1

I Universität Leipzig, Institut für Mineralogie, Kristallographie und Materialwissenschaft, Schamhorststr. 20, D-04275 Leipzig, Germany II Universität Bremen, AK Kristallographie im FB 5 (Geowissenschaften), Klagenfurter Str., D-28359 Bremen, Germany

Received December 7, 1999, CSD-No. 409466

Pb/Bi The excess of PbO as flux increased the Pb-content of the starting composition BaPbo.7Bio.3O3 in the crystals about 22 %. This effect was only determined in Sb-free crystals of the Ba(Pb,Bi,Sb)03 system. The crystals were homogeneous and didn't show zonations, twinnings or intergrowth sections otherwise typical for this kind of perovskites

Discussion Ba(Pbo.9Bio.i)03 single crystals show a tetragonal perovskite- like structure produced by the distortion of the oxygen from their ideal positions creating the glide reflection plane in IAImcm. This space belongs to the one-tilt system (No. 22) without cation ordering [3], Additional measurements with syn- chrotron radiation (HASYLAB at DESY, Hamburg) near the Pb absorption edge in order to seperate Pb and Bi using the anoma- lous dispersion [4] showed a statistical distribution of both cat- on the octahedral site. No exchange of Pb on the Ba site was determined. The space group and oxygen distortion is analogous with results on other Sb-free solution members in the Ba(Pb,Bi,Sb)03 system as described in the literature [5, 6]. Fur- ther investigations of superstructures vs. chemical composition and microscopic reflection colour related to electronic states were carried out [7].

Table 1. Data collection and handling. Abstract BaBi0.10O3Pb0.49, tetragonal, IAImcm (No. 140), Crystal: black, quasi-tetragonal prism, a = 6.0391(9) A, c = 8.605(2) A, V= 313.8 A3, Z = 4, size 0.126x0.126x0.21 mm Wavelength: Mo Ka radiation (0.71073 Ä) R t(F) = 0.034, wR (F2) = 0.081, T= 293 K. 1 g m 1»: 660.69 cm" Diffractometer, scan mode: Siemens P4, co Source of material 20max: 89.88° 3 Single crystals (up to 1 mm ) were grown by PbO-flux in N(/ifci)measured> N(hkl)Umq3094m. , 256 platinum crucibles with Pb- and Bi- and Ba-carbonate as Criterion for /0bs, N(hkl}gc. Us > 2 a(/obs), 247 N ) ftnei'- 12 starting materials cooled down from 1420 K to 1020 K with (param K Programs: SHELXS-86 [7], SHELXL-93 [2] 2-4 K/h [1], The chemical composition BaPbo.90(2)Bio.io(2)C>3 was determined by microprobe analysis (Cameca SX 100). The site occupancy factors were fixed during refinement [2],

Table 2. Atomic coordinates and displacement parameters (in A2).

Atom Site Occ. X y z Un U22 f/33 f/l2 Uli U23

Ba 4 b 0 1/2 1/4 0.0173(3) Un 0.0209(3) 0 0 0 Pb 4c 0.90 0 0 0 0.0111(2) Un 0.0144(2) 0 0 0 Bi 4c 0.10 0 0 0 0.0111 Un 0.0144 0 0 0 O 8 h 0.218(1) x+m 0 0.018(3) Un 0.034(3) 0 0 0.008(4) O 4a 0 0 1/4 0.040(4) Un 0.014(2) 0 0 0

* Correspondence author (e-mail: [email protected]) 466 Ba(Pbo.9Bio.i)03

References 5. Asano, H.; Oda, M.; Endoh, Y.; Hidaka, Y.; Izumi, F.; Ishigaki, T.; Karahashi, K.; Murakami, T.; Watanabe, N.: Neutron powder diffraction 1. Cava, R. J.; Batlogg, B.; Espinosa, G. P.; Ramirez, A. P.; Krajewski, J. J.; from polymorphs of BaPbo.75Bio.25O3. Jpn. J. Appl. Phys. 27 (1988) Peck, Jr., W. F.; Rupp, Jr., L. W.; Cooper, A. S.: Superconductivity at 3.5 1638-1640. K in BaPbo.75Bio.25O3 - why is Tc so low? Nature 339 (1989) 291-294. 6. Bredthauer, J.; Wagner, N.; Jansen, M.: Einkristallzüchtung und 2. Sheldrick, G. M.: SHELXL-93, a program for refining crystal structures. Verfeinerung der Kristallstruktur von BaPb(i_^)Bi(^)03 (x = 0, 0.15). Z. University of Gottingen, Germany 1993. Anorg. Allg. Chem. 593 (1991) 193-199. 3. Glazer, A.: The Classification of Tilted Octahedra in Perovskites. Acta 7. Moretzki, O.: Experimentelle Studien zur Kationen-Ordnung und Crystallogr. B28 (1972) 3384-3392. Überstrukturbildung in Ba(Ba,Pb,Bi,Sb)03-Perowskiten - Röntgen- 4. Wendschuh-Josties, M.: Determination of cation distributions by anoma- beugung und Anwendung der Synchrotronstrahlung. Ph. D. Thesis, Uni- lous dispersion. Z. Kristallogr. 209 (1994) 107-112. versity of Leipzig, Germany 1999. 8. Sheldrick, G. M.: Annealing in SHELX-90: Direct Methods for Larger Structures. Acta Crystallogr. A46 (1990) 467-473.