SOME NEW RESULTS ON LATTICE-DYNAMICS AND PHASE-TRANSITIONS IN PEROVSKITE TYPE COMPOUNDS

Anharmonicity of vibrations in perovskite type (ABO//3) crystals has been studied, including anharmonic vibrations of separate sublattices in BaTiO//3 and SrTiO//3. The above ABO//3 compounds were divided into two groups depending on the character of anharmonicity, this division supporting the earlier classification in terms of ferroelectrically active sublattices (A or B). A detailed study of phase transitions in AB//0//. //5**3** plus B//0//. //5**5** plus O//3 perovskites and in KTaO//3-SrTiO//3 and (Na//0//. //5Bi//0//. //5) TiO//3-CdTiO//3 solid solutions has been carried out. The last results seem to suggest an antiferroelectric mechanism of ″puckering″ transitions.