Константин Жучков » Публикация

Аннотация The approach for extracting information on the directions and values of atomic displacements from the ideal positions in perovskite type compounds is proposed using EXAFS spectra. It is shown that reliable information can be obtained analysing the discrepancy factor between theoretical and experimental Fourier Transformants (FT) for different models of atomic displacements, generated using the value of averaged atomic displacement, provided by X-ray diffraction. By this approach, the rhombohedral local distortion in cubic phase of KNbO3 is revealed. In tetragonal phase of KNbO3 the minimum of discrepancy factor is obtained in assumption that Nb is shifted by 0.19 Å along [211] direction. These results are shown to be stable under the effects of atoms anharmonicity motion, simulated trough the cumulant expansion by variation of the C4-coeficient value. It is shown that strong difference in Im(FT) remains under all possible C4 values, which makes Im(FT) to be reliable probe for B atom displacement, independent of radial distribution function asymmetry.