Defect chemistry and oxygen nonstoichiometry of CeBaFe2O5.5

Highlights: • Synthesis of double-cell perovskite CeBaFe₂O_5.5+w. • Nonostoichiometry description vs T and p_O2 via point-defect equilibria. • Brouwer diagrams of point-defect concentrations versus p_O2. While lanthanoids Ln=Gd to Pr form Ba–Ln ordered double-cell iron perovskites with a wide equilibrium nonstoichiometry from LnBaFe₂O₅ to over O_5.5, the Ce variant of this study no longer forms the CeBaFe₂O₅ composition. Point-defect equilibria behind oxygen nonstoichiometry of the Ce^IIIBaFe^III₂O_5.5 that forms are studied by quenching from flowing gas of controlled oxygen partial pressures p_O2 and temperatures. Their thermodynamic parameters are evaluated on the defect model of pure undoped Ce^IIIBaFe^III₂O_5.5 with an electronic-defect pair e′ and h^• , anion-Frenkel pair O_i′′ and v_O^{• •} , and redox behavior at equilibrium with oxygen in the reaction atmospheres to fit the experimentally determined nonstoichiometry.