The regular approach for identifying the atomic displacements in ABO3 crystals and its application to high-temperature phases of KNbO3

The approach for identifying the atomic displacements from the ideal positions in perovskite structure is proposed, based: on characteristic features in the Fourier Transforms (FT) for different models of atomic displacements and on the results of EXAFS calculations for alternative models of ideal structure distortions, generated using the value of averaged atomic displacement provided by diffraction methods. The approach is applied to study the local structure distortions in tetragonal and cubic phases of KNbO3. The effect of anharmonic motion of atoms on the obtained structure information is simulated through the cumulant expansion.