Polarized XAFS study of KNbO3 local structure

Nb positions in KNbO3 crystal were determined at room temperature via polarized Nb K-XAFS measurements. It has been revealed that the direction of Nb displacement in orthorhombic phase is very close to polar axis direction. This refute eight-site model which assumes that Nb atoms are disordered among several equivalent positions and phase transition are of order-disorder type. Analysis of polarized XAFS data showed that only slight disorder among close positions is possible. The distance between these positions is of an order of temperature atomic displacements, so the disorder, if any, is likely of dynamic nature. Results obtained are in perfect agreement with X-ray diffraction data.