Defect Thermodynamic Modeling of Triple Conducting Perovskites (La,Ba)Fe_1-xM_xO_3-δ for Proton-Conducting Solid-Oxide Cells

Both the experimental and first-principles modeling results revealed the dependence of defect energetics on oxygen non-stoichiometry and magnetic coupling of Fe in the Fe-based perovskite oxides. A generalized defect thermodynamic model of the proton-conducting (La,Ba)Fe 1-x M x O 3-δ perovskite oxide is developed to allow inclusion of nonlinear δ dependent terms in three key defect reaction energies, namely, the oxygen vacancy formation, hydration, and charge disproportionation reactions. A transition from a large polaron description at lower δ values to a small polaron expression at higher δ is also considered in our analysis. Based on the functional forms of defect energetics on δ as guided by first principles modeling and literature data, the Brouwer diagrams of BaFe 0.9 Y 0.1 O 3-δ are assessed to provide information on electronic and ionic defect concentration (including the proton species) as a function of O 2 and H 2 O pressure at different temperatures for solid-oxide cell applications.