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Crystal Structure of High-Temperature Paraelectric Phase in Bi-Layered Perovskite Sr 0.85 Bi 2.1 Ta 2 O 9

2000; Institute of Physics; Volume: 39; Issue: 9S Linguagem: Inglês

10.1143/jjap.39.5711

1347-4065

Akira Onodera Akira Onodera, Takayuki Kubo Takayuki Kubo, K. Yoshio, Seiji Kojima, Haruyasu Yamashita, Toshihiko Takama,

Multiferroics and related materials

The crystal structure of Bi-layered perovskite Sr 0.85 Bi 2.1 Ta 2 O 9 was determined at 750 K by X-ray Rietveld analysis. Sr 0.85 Bi 2.1 Ta 2 O 9 with space group A2 1 am at room temperature transforms to the paraelectric phase above 670 K, passing through a probable intermediate state at 510 K. Assuming two possible orthorhombic Fmmm and tetragonal I4/mmm space groups, analysis of the crystal structure of the paraelectric phase gave the final discrepancy factors R w p of 11.3% and 9.9%, respectively. Examination of possible reflections and peak positions at high-angles proved that the true space group is I4/mmm for the high temperature paraelectric phase. The lattice constants are a =3.927 (1), c =25.142 (1) Å at 750 K. The TaO 6 octahedron is not perfect and is slightly distorted along the c -axis, having the dipole moment of 0.478 debye.