Systematic investigation on structure stability and oxygen permeability of Sr-doped BaCo0.7Fe0.2Nb0.1O3−δ ceramic membranes

Ba1−xSrxCo0.7Fe0.2Nb0.1O3−δ (BSCFN, 0.0 ≤ x ≤ 0.4) materials were synthesized by the conventional solid-state reaction process for oxygen separation application. The influences of strontium doping in BSCFN oxides on phase structure stability, oxygen nonstoichiometry, electrical conductivity and oxygen permeation behavior were systematically investigated. Improved cubic structure stability under reducing atmosphere and structure reversibility in alternative oxidizing/reducing atmospheres were obtained via strontium doping strategy. Strontium introduction effectively suppressed the phase transformation from cubic to hexagonal under high temperature and harsh atmosphere conditions. Strontium doping increased the electrical conductivity, however, slightly decreased the oxygen permeability. Structural parameters played an important role in charge compensation mechanism and oxygen permeability. Ba0.6Sr0.4Co0.7Fe0.2Nb0.1O3−δ membranes exhibited good structural stability and the sample with a thickness of 1 mm had a high level of oxygen permeation flux of 1.31 mL cm−2 min−1 at 900 °C under an Air/He gradient. It was demonstrated that the oxygen bulk diffusion was the rate-controlling step for oxygen permeation in BSCFN (x = 0.4) membranes when the thickness was higher than 1 mm, while the oxygen surface exchange process should be taken into consideration when the thickness was less than 1 mm.