Effect of oxygen vacancies on electrical conductivity of La0.5Sr0.5FeO3−δ from first-principles calculations

We use first-principles density functional theory calculations to understand how oxygen vacancies degrade the electrical conductivity of mixed ionic-electronic conductor (MIEC) at low oxygen partial pressure (PO2). Analysis focused on La0.5Sr0.5FeO3−δ, which shows the highest mixed conductivity among cobalt-free iron-based perovskite oxides. Calculation results show that hole compensation by electrons released from oxygen vacancies lowers the electrical conductivity and eventually leads to metal-to-semiconductor transition at low PO2. Analyses of effective mass change and charge-density show that holes are the major charge carrier of electrical conductivity, but the contribution of electrons to conductivity increases as temperature increases. We suggest several possible ways to reduce the degradation of electrical conductivity at low PO2. Our results provide guidelines to design highly effective oxygen-selective membranes.