First-principles calculations of an oxygen deficient Σ $equal$ 3(111)[10] grain boundary in strontium titanate

An oxygen vacancy in a Σ = 3(111)[10 ] grain boundary (GB) in SrTiO 3 is modelled using DFT plane-wave pseudopotential methods. The formation energy of the vacancy in the boundary is found to depend on its charge state and on the electron chemical potential. There is a strong driving force for segregation when the vacancy is in the charge neutral state and this results in an electrostatic potential barrier at the GB. The vacancy is found to act as a donor and the GB becomes n-type. The defect induces small atomic relaxations in an otherwise highly ordered GB structure.