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 LiNbO3-delta (delta = 0.083/f.u.), electrons are itinerant, while in ZnTiO3-delta and ZnSnO3-delta (delta = 0.083/f.u.) the electrons are localized. These results provide guidance for the application of oxygen vacancies in LiNbO3-type ferroelectric material devices.