A study on the formation and migration of oxygen vacancies in Ba0.5Sr0.5Co0.75Fe0.25O3-δ perovskite surfaces by first-principles modelling

Abstract Mixed conducting perovskites such as Ba 0.5 Sr 0.5 Co 0.75 Fe 0.25 O 3-δ (BSCF) are attracting interest for solid oxide fuel cells (SOFCs). Electrochemical behaviors of BSCF surfaces, compared to a bulk one, have not been investigated yet. In this paper, electrochemical properties of BSCF were investigated by density functional theory (DFT). We calculated barriers of the (011) BSCF terminated by Sr Co O, and compared them with the bulk values. We found that the oxygen vacancy migration energies within 6.87–9.59 A in depth in the slab are nearly similar to the bulk values. The surface oxygen vacancy migration energies in (011) and (001) slabs of BSCF were compared. They have two values in the (011) BSCF and vacancies migrate under two models, which are different in terms of their geometries. However, there is a single value for the oxygen vacancy migration energy in the (001) BSCF. The surface oxygen vacancy formation energy of the (011) BSCF terminated by the O O surface is much less than the bulk value. Oxygen vacancies can simply migrate to the O O surface, because the migration energy required for jumping to the surface is very small. Therefore, the presence and diffusion of vacancies in layers close to the O O surface are more probable.