Comparison of carrier doping in ZnSnO₃ and ZnTiO₃ from first principles

Ferroelectric materials have attracted increasing attention due to their rich properties. Unlike perovskite ferroelectric oxides, in the LiNbO₃-type ferroelectric oxides of ABO₃, ferroelectrically active cations are not necessary. While the effects of carrier doping on perovskite ferroelectric oxides have been extensively studied, the studies on LiNbO₃-type ferroelectric oxides are rare. We consider two LiNbO₃-type ferroelectric oxides ZnSnO₃ and ZnTiO₃, where the former has no ferroelectrically active cation and the latter has ferroelectrically active cation Ti⁴⁺, and study the effect of carrier doping by performing first-principles calculations. Comparison results indicate that the B-site cation has significant effects on the polar distortion in LN-type ferroelectrics. Our studies show that LN-type materials can maintain the coexistence of ferroelectricity and conductance over a very wide range of concentrations. The polar displacement is even enhanced under hole doping. More importantly, ZnSnO₃ can be doped by electrons up to a high level to realize the conducting ferroelectrics of high mobility due to its isolated s conduction band.