In this work, we investigate the effect of partial substitution of bismuth oxide on BaSc0.1Co0.9O3-delta perovskite membranes. Doping was carried out in the A-site (Ba1-xBixSc0.1Co0.9O3-delta) and B-site (BaBixSc0.1Co0.9-xO3-delta). Bi doping at or below 10% (x <= 0.10) in both sites resulted in significant increase of oxygen flux, up to two orders of magnitude at the low to medium temperature range (650-850 degrees C) as compared to non-doped disk membranes. Among all compositions, B-site doped x = 0.05 showed the highest oxygen fluxes, reaching 2.17 ml min(-1) cm(-2) at 950 degrees C. These results suggest that Bi doping at or below 10% conferred superior ionic oxygen diffusion transport, owing to the formation of cubic structures. Further increases in the Bi-doping amount formed non-cubic structure delivering very low oxygen fluxes. The structure transition phenomena from non-cubic to cubic crystal lattices occurred for non-doped and A-site doped membrane with 20 and 30% mole bismuth oxide in excess of 800 degrees C, concomitantly with increases in oxygen fluxes and sharp rise of electrical conductivity. A-site and B-site doped x=0.05 compounds exposed to nitrogen atmosphere at 850 degrees C for 7 days showed reasonable stable structure. (C) 2010 Elsevier B.V. All rights reserved.