Sn-containing SrCo0.8Fe0.2O3-delta (SCF) oxygen-permeable dense ceramic membranes were prepared and characterized. The solid solubility of Sn in SCF was found not higher than 2.5 mol%; beyond that value, the membrane existed as a composite comprising an oxygen-permeable SCF phase and oxygen-imperious SrSnO3 (SS) phase. The inclusion of 15 mol% of SS phase in SCF gave rise to an increase of sintering temperature from 1100 to 1280 degreesC. By exposing a 1.2-mm-thick composite to air at one side and flowing helium at the other side, oxygen permeated through the membrane at rates of 1.3 x 10(-6) and 5 x 10(-8) mol cm(-2) s(-1) at 1000 and 560 degreesC, respectively. The Arrhenius plot of oxygen permeation flux showed a bending at 737 degreesC for the composite, about 80 degreesC lower than that for the single-phase SCE Moreover, the oxygen permeability of the composite decreased less pronouncedly with decreasing temperature than that for SCF, especially in the temperature range below the bending point. The composite also showed a reduced thermal expansion compared with SCF, which would improve the mechanical compatibility of the membrane with other components in a membrane assembly. (C) 2003 Elsevier B.V All rights reserved.