Role of intrinsic defects in cubic NaNbO3: A computational study based on hybrid density-functional theory

Antiferroelectric NaNbO3 is a candidate material for application in high-energy density dielectric capacitors. In this context, various doping strategies have been used for installing the desired narrow double P–E loop behavior in this lead-free material. However, controlled doping requires a detailed understanding of the type and population of intrinsic defects, which have not been studied so far. In this study, we, therefore, calculate formation energies, electronic transition levels, and doping behavior of intrinsic defects in cubic NaNbO3 by means of electronic structure calculations based on density functional theory using a hybrid exchange-correlation functional (HSE06) and finite-size correction. The results show that the dominant defects are Na and O vacancies, and that the material is an n-type semiconductor for almost all oxygen partial pressures. Additionally, we predict the presence of a defect complex (VNa– VO– VNa) consisting of two Na vacancies and one O vacancy in two possible structures, which is stable for n- or p-type doping conditions.