Partially Zr-substituted BaFe 1-yZr yO 3-δ membranes were developed as a Co-free oxygen permeable membrane. In order to stabilize the cubic perovskite structure, Fe sites in BaFeO 3-δ were partially substituted with Zr 4+. In the substitution range of y=0.01-0.1, the cubic perovskite structure was stabilized even at room temperature. Among the membranes prepared, a BaFe 0.975Zr 0.025O3 -δ material (y=0.025) showed the highest oxygen permeation flux of 1.30 cm3 (standard temperature pressure) min-1 cm-2 at 930°C under an air/He gradient. The oxygen permeation flux was higher than that of partially Ce-substituted BaFe 1-yCe yO 3-δ membranes reported previously. From the results obtained by chemical and scanning electron microscope analyses, it appears that the oxygen permeability for BaFe 1-yZr yO 3-δ membranes was well correlated with the amount of oxygen defects in the lattice as well as the grain size. In addition, the oxygen permeation flux of the BaFe 0.975Zr 0.025O3 -δ membrane was significantly increased after decreasing the thickness of the membrane from 2.0 to 0.4 mm. For thin membranes (0.4-1.0 mm), the thickness dependence of the oxygen permeability deviated from the Wagner equation, suggesting that the oxygen permeation of BaFe 0.975Zr 0.025O3 -δ is controlled by not only bulk diffusion of oxide ions but also their surface reactions.
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