IDENTIFICATION OF ATOM DISPLACEMENT DIRECTIONS IN ABO(3) COMPOUNDS BYEXAFS

Ab initio simulations of Nb K-XAFS in crystals with well known structu res - LiNbO3, NaNbO3 at T = 300 K, rhombohedral KNbO3 and the analysis of their Fourier-transformants (FT) permit to propose the probe for i dentification of Nb displacements from the centre of oxygen-octahedron for two typical types of the ideal perovskite structure distortions. The stability of the obtained probe under the variations of DW-factors is revealed. The application of this probe provides the regular appro ach to choose the model of radial atomic distribution function used th en for precise determination of structure parameters. With its help th e Nb displacement in orthorhombic phase of KNbO3 is identified removin g the contradiction between X-ray diffraction and EXAFS data.