An X-ray Study of Thermal Atomic Vibrations in Oxygen-Octahedra Compounds

An X-ray diffraction study of ferro-, antiferro- and paraelectrics with perovskite, elpasolite and pyrochlore type structures has been carried out. The influence of anharmonic thermal atomic vibration on temperature dependences of temperature factors of individual sublattices, Debye temperatures and logarithms of relative integrated intensities has been studied. The potential parameters of individual sublattices α k and γ k have been calculated. The conclusion has been made that in perovskites ABO 3 (A=Pb, B=Ti, Zr), elpasolites A 2 Ca 2+ B 6+ O 6 (A=Ba, B 6+ =Re, Te) and pyrochlores A 2 B 2 O 6 X (A=Cd, B=Nb, X=O, S), A-sublattice should be considered as ferroelectrically active one, and that deviations from harmonic behaviour for A-cations seem to be appreciable.