Structural Studies of Doped Lanthanum Orthoferrites of Interest for SOFCs

Traditional LSM (La1-xSrxMnO3-w) SOFC cathode material shows some drawbacks operating below 800 degrees C, in particular poor oxygen ion conduction, which limits the active area of the electrode to the three phase boundary (TPB) between electrolyte, electrode and gas phase at the interface. A strategy to overcome this problem consists in the development of materials with both good oxygen ion and electronic conductivity, in which oxygen ions catalytically dissociated on the surface are able to reach the electrolyte by diffusion in the bulk of the cathode. La1-xSrxFeO3-w has been proposed as possible SOFC cathode, in search for a high activity at lower temperatures with respect to LSM. The aim of the work is the structural study of alternative cathodic materials for intermediate temperature solid oxide fuel cells, mainly based on ABO(3) perovskite-type lanthanum ferrite. Within this framework the effects of A (La)-site doped with Sr or B (Fe)-site doped with Ta on the crystal structures of these materials were investigated by X-ray powder diffraction (XRPD). In conjunction with the experimental results, the microscopic mechanisms of the doping effect were discussed providing deeper understanding into structure-property relations.