Mixed conducting SrCo0.9Nb0.1O3-delta perovskite is a newly developed promising ceramic membrane material for air separation. In this work, SrCo0.9Nb0.1O3-delta was further optimized by the introduction of Ba to partially replace Sr in the A-site of the perovskite structure. The phase structure, phase stability, carbonate formation rate under carbon dioxide atmosphere, electrical conductivity, oxygen desorption properties, and oxygen permeation properties of BaxSr1-xCo0.9Nb0.1O3-delta (BSCNx) with varying Ba2+ doping level were systematically investigated. Pure phase cubic perovskite was formed at x=0.0-0.8. BSCNx (x=0.0-0.8) can be stably operated in atmospheres with oxygen partial pressure varying from at least 1 atm to as low as 10(-5) atm (Ar atmosphere). The barium doping concentration had a significant effect on electrical conductivity and oxygen permeability of the membranes. BSCN0.6 had the highest oxygen permeation flux of 2.67 x 10(-6) mol cm(-2) S-1 for 0.87 mm thickness at 900 degrees C and the highest oxygen ionic conductivity of 1.38 S cm(-1) at 900 degrees C. (C) 2009 Elsevier B.V. All rights reserved.