Oxygen permeation properties of partially A-site substituted BaFe O3-δ perovskites

To explore oxygen permeable materials, oxygen permeation properties of partially A-site substituted BaFe O_3-δ perovskites were investigated. Ba sites in BaFe O_3-δ were substituted with cations such as Na, Rb, Ca, Y, and La by 5%. The partial substitution with Ca, Y, and La, whose ionic radii are smaller than that of Ba, succeeded in stabilizing a cubic perovskite structure that is a highly oxygen permeable phase, as revealed by X-ray diffraction analysis. This can be explained in terms of a decrease in the tolerance factor (t). Among the Ba_0.95 M _0.05 Fe O_3-δ (M = Na, Rb, Ca, Y, and La) membranes tested, Ba_0.95 La_0.05 Fe O_3-δ showed the highest oxygen permeability at 600-930°C, owing to the stabilization of the cubic phase without the formation of impurity phases. From chemical analysis, the oxygen permeability of Ba_1-x La_x Fe O _3-δ membranes was correlated with the amount of oxygen defects (δ) in the lattice. The oxygen permeation flux of Ba_0.95 La_0.05 Fe O_3-δ membrane was significantly increased by reducing its thickness. Furthermore, a Ba_0.975 La_0.025 Fe O_3-δ membrane exhibited good phase stability under He flow at elevated temperatures. The obtained results indicate the promising properties of Ba_1-x La_x Fe O3-δ membranes as a cobalt-free material that has a high oxygen permeability, good phase stability, and low cost.