Structural stability and oxygen permeability of BaCo1-xNbxO3-δ ceramic membranes for air separation

BaCo1-xNbxO3-delta (BCNx, x = 0.1-0.2) membranes were synthesized through conventional solid-phase reactions. The introduction of niobium facilitates the formation of the cubic perovskite structure and decreases oxygen nonstoichiometry. BCNx membranes possess higher oxygen permeation flux compared with BaCo0.7Fe0.2Nb0.1O3-delta membrane at the same condition. A stable permeation flux as high as 2.61 ml cm(-2) min(-1) is obtained through BaCo0.9Nb0.1O3-delta membrane at 900 degrees C under the Air/He gradient. Long-time permeation study shows that the oxygen fluxes of BCNx membranes are stable at 900 degrees C but degrade slowly with time at 850 degrees C. XRD and TG-DSC results indicate that the degradation behavior occured at 850 degrees C is due to the phase transition from the cubic perovskite to monoclinic or orthorhombic structure, which is governed by the oxygen partial pressure and temperature. The oxidation of cobalt ion is considered to be the nature for the phase transition, which makes the tolerance factor increasing and results in structural destabilization. (C) 2015 Elsevier B.V. All rights reserved.