HIGH-TEMPERATURE ELECTRICAL-PROPERTIES AND DEFECT CHEMISTRY OF LA2-XCAXCUO4-Y SUPERCONDUCTORS .2. DEFECT STRUCTURE MODELING

The defect structure of La2-xCaxCuO4-y superconductors was examined by fitting electrical property and oxygen nonstoichiometry data to a var iety of models. Those involving charged oxygen vacancies, whether isol ated or associated, were inadequate for simultaneously describing the dependence of both properties on doping level and oxygen partial press ure. Neutral oxygen vacancies and their association with dopants were invoked, resulting in a successful reconciliation of all existing expe rimental data. The defect types and configurations can be rationalized in terms of the bond-mismatch between the (LaO)(2) and CuO2 layers in the La2CuO4 structure. The defect associates proposed may be responsi ble for the suppression in T-c relative to the La2-xBaxCuO4-y and La2- xSrxCuO4-y systems.