Defect chemistry in La/Sr-based oxyhydrides

Oxyhydrides in the series La_2-ySr_yLiH_1+yO_3-y have attracted interest for solid-state hydrogen electrolytes on account of their high H^- ionic conductivity. Here, we use first-principles calculations to examine the prevalence of native point defects in La₂LiHO₃ and Sr₂LiH₃O and connect our results to ionic transport properties. We find that both oxyhydrides have high concentrations of point defects. Sr₂LiH₃O, in particular, experiences a stabilizing effect from disorder caused by the presence of pairs of compensating species, such as O_H^- and V_H⁺, or O_H^- and H_i⁺. V_H⁺ serves as the most important point defect for ionic conduction; its presence explains the high conductivity in Sr₂LiH₃O. We identify O-rich and moderately H-rich synthesis conditions as optimal for ensuring stability and maximizing ionic conductivity.