Perovskites are used as state of the art solid oxide fuel cell (SOFC) cathode materials. The requirements of cathode materials include long term stability at the oxygen partial pressures and temperature of SOFC operation and production, good electrical conductivity, matching thermal expansion coefficient as well as various microstructural criteria. A further requirement is good catalytic activity for oxygen reduction, which seems to be linked to the oxygen ion conductivity, which is again linked to the oxygen deficiency of the perovskite.
We have assessed the La-Mn-O and Sr-Mn-O systems and extrapolated to the La-Sr-Mn-O system using the CALPHAD approach. We focus on the perovskite phase that is modelled using the compound energy formalism and find that the rather complex defect chemistry of the (La, Sr)MnO3 perovskite can be predicted quite well by extrapolating the properties of the perovskites LaMnO3 SrMnO3 as long as the correct model for the defect chemistry is chosen! We further demonstrate the usefulness of such an assessment as it allows very quick and simple overview of the equilibrium defect chemistry of a perovskite of any possible composition at any temperature or oxygen partial pressure. This is of course very valuable information, as it allows at least qualitative predictions on electronic conductivity, ionic conductivity and even bulk diffusion of the perovskite.