Oxygen Nonstoichiometry and Defect Structure Analysis of Sr- and Fe-Substituted LaCoO3

A defect chemical model for the behavior of acceptor and donor-doped LaCoO3 as a function of oxygen pressure is proposed. The nonstoichiometric deviation was calculated as a function of oxygen partial pressure, pO2, at different temperatures. Oxygen nonstoichiometries of various B-site mixed LaCoO3-based ceramics were compared with those of A-site substituted perovskite-type oxides. The defect structure of complex oxides was described within the point defects approach. The results show that the conductivity was dependent of pO2 and proportional to the dopant concentration on A and B sites. Stability regimes and compensation mechanisms at various oxygen partial pressures and at various temperatures are proposed. This model examines also the charge compensation mechanisms that dominate under the different regimes and their implications for transport properties. From equilibrium constants, partial molar enthalpy and partial molar entropy of oxygen in La1-xSrxCo1-yFeyO3-δ were calculated.