Cobalt-free perovskite-type oxides with the nominal composition of BaNbyFe1-yO3-delta(y=0.025-0.20) are synthesized and evaluated as materials used in ceramic membranes for oxygen separation. The effects of Nb-doping on the crystal structure, surface morphology, electrical conductivity, chemical built diffusion and surface exchange, and oxygen permeability of the oxides are systematically investigated using XRD, SEM, four-probe DC conductivity, electrical conductivity relaxation technique, and oxygen permeation studies. A small amount of Nb-doping induces a sharp increase in electrical conductivity. A further increase in the Nb-doping amount, however, lowers the electrical conductivity as a result of the blocking effect of Nb5+ on electronic conduction. A small amount of Nb-doping has less impact on the sintering capability. From the oxygen permeation test, it was found that Nb-doping could significantly enhance the oxygen permeability, especially below 750 degrees C. Among all of the compositions. BaNb0.05Fe0.95O3-delta shows the highest oxygen permeation fluxes, reaching 1.35 and 0.61 mL cm(-2) min(-1) for a membrane with a thickness of 1.0 mm at 900 and 700 degrees C, respectively. Furthermore, the membrane is rate-controlled mainly by bulk diffusion, indicating the potential to further improve the oxygen permeation flux via a thinner membrane. (C) 2013 Elsevier B.V. All rights reserved.