The temperature dependence for the third shell's Fourier-peak of Nb-EXAFS in KNbO₃ as additional source of information on the local atomic structure

The information on the structure of tetragonal KNbO₃ is extracted from the temperature dependence of the third shell's Fourier-peak of Nb-EXAFS. It is shown that this dependence can be explained by two effects: 1) rigid rotations of the O₆-octahedron and 2) increase of the third shell's DW-parameter. However, diffraction data on the temperature dependence of the DW-parameter permit us to conclude that the last effect only is sufficient and the O₆-octahedron rotation doesn't occur in the high-temperature phases of KNbO₃. Using EXAFS it is revealed that in the neighboring cells Nb-atoms are parallel shifted closely to [211] direction in tetragonal phase.