The regular approach for identifying the atomic displacements in ABO(3) crystals and its application to high-temperature phases of KNbO3

The approach for identifying the atomic displacements from the ideal positi ons 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 s tructure distortions, generated using the value of averaged atomic displace ment provided by diffraction methods. The approach is applied to study the local structure distortions in tetragonal and cubic phases of KNbO3. The ef fect of anharmonic motion of atoms on the obtained structure information is simulated through the cumulant expansion.