LOCAL LATTICE INSTABILITY AND IONIC TRANSPORT IN HIGH-TEMPERATURE SUPERCONDUCTORS

Ionic transport, a characteristic feature of superionic conductors, is analyzed microscopically for the RBa2CU3O7-delta (R=rare earth) high- temperature superconductors. The electronic correlation effects are co nsidered to be responsible for the formation of a local double-well po tential for apical oxygen, which in its turn results in a decrease of the activation energy for interstitial chain oxygen defects. The behav ior of the double well upon reduction of the oxygen content is discuss ed and its possible manifestation in the low-frequency dynamical respo nse is considered.