Computational investigation of defect segregation at the (001) surface of BaCeO3 and BaZrO3: the role of metal–oxygen bond strength in controlling vacancy segregation

Abstract

The low proton grain boundary conductivity observed in perovskites such as BaZrO₃ is generally attributed to a positive grain boundary core charge that repels protonic defects away from the interfacial region. This core charge develops from the segregation of positively charged defects to the grain boundary interface. Here, the results of a density function theory investigation of defect segregation at two (001) surfaces of BaCeO₃ and BaZrO₃ perovskites are presented that give insight into this phenomenon. Yttrium dopant and oxygen vacancy segregation were explored independently and synergistically at these simplified perovskite–vacuum interfaces in order to establish the enthalpic driving forces that promote defect segregation at different surfaces caused by intrinsic material properties. It was found that dopant segregation strongly influences the stability of oxygen vacancies at the perovskite surface because of favorable pairing between dopants and vacancies. Furthermore, the results demonstrate that selecting materials on the basis of metal–oxygen bond strengths offers a potential means of engineering perovskites to mitigate the development of a strong positively charged grain boundary core.