Transport properties and defect chemistry of high-Tc-superconductors

We discuss novel electrochemical data on Bi2Sr2CaCu2O8-delta (BSCCO) at high temperature, where equilibrium with the oxygen containing neighboring phase is established. Measurements of the electronic conductivity as a function of oxygen partial pressure and temperature convey information about the defect chemistry. Careful investigation of the electrochemical polarization on glass-sealed cells allows the determination of the ionic conductivity. The investigation of the instationary response of the electrochemical polarization measurements enables us to determine the chemical diffusion coefficients. The defect chemistry can be understood by an anti-frenkel disorder of the oxygen sublattice. In Bi2Sr2CaCu2O8+delta interactions between ionic and electronic charge carriers are important. The results are summarized in the framework of simple defect models which are discussed in the context of former results on (La, Sr)(2)CuO4 and YBa2Cu3O6+delta.