Local lattice instability and ionic transport in high-temperature superconductors

Ionic transport, a characteristic feature of superionic conductors, is analyzed microscopically for the RBa2Cu3O{7-Σ} (R = rare earth) high-temperature superconductors. The electronic correlation effects are considered to be responsible for the formation of a local double-well potential for apical oxygen, which in its turn results in a decrease of the activation energy for interstitial chain oxygen defects. The behavior of the double well upon reduction of the oxygen content is discussed and its possible manifestation in the low-frequency dynamical response is considered.