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 direct ion of Nb displacement in orthorhombic phase is very close to polar ax is direction. This refute eight-site model which assumes that Nb atoms are disordered among several equivalent positions and phase transitio n are of order-disorder type. Analysis of polarized XAFS data showed t hat only slight disorder among close positions is possible. The distan ce between these positions is of an order of temperature atomic displa cements, so the disorder, if any, is likely of dynamic nature. Results obtained are in perfect agreement with X-ray diffraction data.