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We optimize the niobium doping concentration in BaCo0.7Fe0.3−x Nb x O3−δ (x = 0.08−0.14) and find the increase of niobium content improves the chemical stability of oxides significantly but influences the oxygen permeation of compounds little. The effects of niobium doping on BaCo0.7Fe0.3−x Nb x O3−δ compounds were evaluated by experiments and explained with the help of computational modeling. When niobium is doped into BaCo0.7Fe0.3−x Nb x O3−δ compounds, the energy states of Nb ions locate far above the Fermi level, so the released electrons by oxygen vacancy formation under reducing atmosphere would hardly occupy the Nb states. The Ba−Nb−Ba opening is the more favorable channel for oxygen ion migration than Ba−Fe−Ba opening; therefore, the substitution of iron by niobium enhances the ionic mobility in compounds through lowering the migration barrier of oxygen ion in lattice. Therefore, the positive effects of niobium doping on oxygen mobility would compensate its negative impacts on oxygen defects.

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