First-principles study of oxygen vacancies in LiNbO₃-type ferroelectrics

LiNbO₃-type ferroelectric oxides, as an important class of non-centrosymmetric compounds, have received great attention due to their important and rich properties. Although oxygen vacancies are widely present, studies of them in LiNbO₃-type ferroelectric oxides are rare. In this article, we consider three representative LiNbO₃-type ferroelectric oxide materials LiNbO₃, ZnTiO₃ and ZnSnO₃ to study the impact of oxygen vacancy doping using first principles calculations. LiNbO₃ and ZnTiO₃ have ferroelectrically active cations Nb⁵⁺ and Ti⁴⁺, while ZnSnO₃ does not have ferroelectrically active cations. The distribution of the oxygen vacancy induced electrons are quite different in the three materials even though they have similar structures. In oxygen deficient LiNbO_3- (δ = 0.083/f.u.), electrons are itinerant, while in ZnTiO_3- and ZnSnO_3- (δ = 0.083/f.u.) the electrons are localized. These results provide guidance for the application of oxygen vacancies in LiNbO₃-type ferroelectric material devices.