Investigation of phase structure, sintering, and permeability of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes

The high temperature phase structures of the perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) were characterized by in situ high-temperature X-ray diffraction, which revealed that BSCF exhibits a good phase reversibility and structure stability in air from room temperature to 1273 K. The XRD patterns of BSCF oxide at 1173 K in different atmospheres (air, 2% O2 in Ar and pure Ar) indicated that BSCF possesses an excellent phase stability at high temperatures not only in air but also in pure Ar. From the plot of the lattice constant against the temperature, the thermal expansion coefficient of BSCF was determined to be 11.5 × 10−6 K−1, which is smaller than that of SrCo0.8Fe0.2O3−δ (SCF) (17.9 × 10−6 K−1). Microstructures of the membranes sintered under different conditions were characterized by scanning electron microscopy (SEM). The effect of microstructure on the oxygen permeation flux through BSCF was observed by measuring the oxygen permeation flux using samples sintered under different conditions. The oxygen permeation flux increased considerably with the increase of the grain size of the membrane.