The influence of cation substitution on the transition metal oxidation states, oxygen nonstoichiometry and oxygen transport properties of Ba(Co,Fe,Nb)O3−δ perovskites was investigated with room temperature X-ray diffraction, X-ray absorption near edge structure and high temperature oxygen permeation measurements. Results show that substitution of Fe for Co was accompanied by a decrease in the lattice constant, whereas Nb substitution leads to the opposite trend. With increasing Fe and/or Nb content, the oxygen permeation flux decreases, whereas the apparent activation energy of the oxygen permeation increases. The oxidation state of Co was smaller than +3 and susceptible to the variation of cation composition. In contrast, the oxidation states of Fe and Nb were larger than +3 and close to +5, respectively, and almost independent of the composition. The influence of Fe and Nb contents on the oxygen transport properties was discussed in terms of the oxygen stoichiometry and metal-oxygen bonding.

Oxygen Permeation and Oxidation States of Transition Metals in (Fe, Nb)-Doped BaCoO3-δ Perovskites. J.Yi, J.Brendt, M.Schroeder, M.Martin: Journal of Membrane Science, 2012, 387-388, 17-23