Extended x-ray absorption fine-structure indication of a double-well potential for oxygen vibration in Ba1-xKxBiO3

X-ray absorption spectra of the oxide systems Ba1-xKxBiO3 and BaPbO3 above the Bi and Pb L-3 absorption edges were investigated. It was shown that oxy gen ions move in a double-well potential and their oscillations are correla ted with the charge-carrier movement. The observed breathing-like oxygen vi bration in the double-well potential with large amplitude and low frequency causes the strong electron-phonon coupling and high T-c-values for doped B aBiO3. Based on the experimental data, a model of the relationship of the e lectronic and local crystal structures is proposed that is in good agreemen t with the results from transport measurements, and inelastic neutron and e lectron scattering, Raman scattering, and photoemission spectroscopy. In th e framework of the model, the possible reasons for the superconductivity in perovskite-like oxides are discussed.