Polarized XAFS study of the atomic displacements and phase transitions in KNbO3

Polarized XAFS technique has been applied for the determination of the dire ctions and the values of the Nb displacements relative to the centers of ox ygen octahedra in KNbO3. The temperature dependence of the both EXAFS and X ANES spectra were analyzed in order To reveal the role of disorder in the p hase transitions of this compound. The polarized XAFS appeared to be enough sensitive to detect the delicate balance between order-disorder and displa cive mechanisms of the phase transitions in KNbO3 The magnitude of the pre- edge peak on the Nb K-XAFS spectra was found to be highly correlated with t he value of the Nb off-center displacement, obtained by fitting of the EXAF S spectra.