Sulfur-doping effects on oxygen vacancy formation in LaBO₃ (B = Fe, Co, and Ni) perovskites

Oxygen vacancy (V_O) formation in perovskites plays an important role in improving their functional applications. Using density functional theory calculations, we investigated the effect of sulfur (S) doping on V_O formation in LaBO₃ (B = Fe, Co, and Ni) perovskites, considering the HS, IS, and LS states of Co ions in LaCoO₃ to examine the influence of spin states. Our results show that the weaker electronegativity of S^2- than that of O^2- leads to a decrease in the magnetic moment of B atoms directly adjacent to the substituted S and an increase in the electrical conductivity of insulating systems. Formation energy (E_f) calculations suggest that S doping is beneficial for V_O formation. In particular, V_Os are more likely to form at oxygen positions adjacent to S ions. Moreover, upon S doping, spin state transition is not a necessary condition to lower the E_f. Instead, the main reason for reducing the E_f of V_Os is the decreased relaxation energy of the lattice following V_O formation. Therefore, we revealed a common mechanism for S-doping-promoted V_O formation, which could be extended to other perovskites.