EXAFS indication of double-well potential for oxygen vibration in Ba_{1-x}K_xBiO_3

Abstract

X-ray absorption spectra of oxide systems Ba_{1-x}K_xBiO_3 and BaPbO_3 above Bi- and Pb-L3 absorption edges were investigated. It was shown that oxygen ions move in double-well potential and their oscillations are correlated with charge carrier movement. Observed breathing-like oxygen vibration in double-well potential with large amplitude and low frequency causes the strong electron-phonon coupling and high Tc values in doped BaBiO_3. Based on the experimental data, the model of relationship of electronic and local crystal structures is proposed that is in a good agreement with the results of transport measurements, inelastic neutron and electron scattering, Raman scattering, and photoemission spectroscopy. In the framework of the model the possible reasons of superconductivity in perovskite-like oxides are discussed.