Modelling oxygen defects in orthorhombic LaMnO₃ and its low index surfaces

LaMnO₃-based perovskites, which have been extensively studied as cathodes for high temperature solid oxide fuel cells (SOFCs), are also of interest for intermediate temperature SOFCs (T = 600-1000 K). Oxygen vacancy formation is required in LaMnO₃ for oxygen diffusion, therefore a low vacancy formation energy is preferable. The stability of the low index surfaces of orthorhombic LaMnO₃ has been investigated, with the {010} surface found to be the most stable. Surface stability was found to be affected by the La and Mn coordination, and the Mn-O bonds cleaved on surface formation. The crystal morphology has been predicted, in order to determine the most likely terminations to be present. The formation of oxygen vacancies in bulk LaMnO₃ and at all of its low index surfaces has been examined, and it has been found that formation of vacancies in the bulk has a high energy, while there is a large variation in formation energies at the low index surfaces, which is likely to lead to segregation of vacancies to the surface of orthorhombic LaMnO₃.