Defect chemistry and oxygen nonstoichiometry of CeBaFe2O5.5

Abstract

While lanthanoids Ln ​= ​Gd to Pr form Ba–Ln ordered double-cell iron perovskites with a wide equilibrium nonstoichiometry from LnBaFe2O5 to over O5.5, the Ce variant of this study no longer forms the CeBaFe2O5 composition. Point-defect equilibria behind oxygen nonstoichiometry of the CeIIIBaFeIII2O5.5 that forms are studied by quenching from flowing gas of controlled oxygen partial pressures pO2 and temperatures. Their thermodynamic parameters are evaluated on the defect model of pure undoped CeIIIBaFeIII2O5.5 with an electronic-defect pair e′ and h•, anion-Frenkel pair Oi′′ and vO••, and redox behavior at equilibrium with oxygen in the reaction atmospheres to fit the experimentally determined nonstoichiometry.