EXAFS spectroscopy of perovskite-type superconducting oxides

On the basis of the investigation of the temperature dependences of EXAFS spectra of the Ba1−xKxBiO3 superconducting oxide, a model of relationship between the local crystalline and electronic structures is proposed. It is found that oxygen ions vibrate in a double-well potential and their vibrations are correlated with the local electron pair transfer. Analogous specific features are also observed in the EXAFS spectra of La2−xSrxCuO4, which gives grounds to extend the proposed model to Cu-based superconductors. The model based on the unified approach makes it possible to explain the ground antiferromagnetic state, the insulator-metal transition, and the occurrence of superconductivity upon doping of La2CuO4 with strontium.