Properties and performance of A-site deficient (Ba_0.5Sr_0.5)_1-xCo_0.8Fe_0.2O_3-δ for oxygen permeating membrane

(Ba_0.5Sr_0.5)_1-xCo_0.8Fe_0.2O_3-δ (BSCF) (x = 0-0.3) oxides were prepared by a combined EDTA-citrate complexing method. The crystal structure, electrical conductivity, sintering behavior and oxygen desorption property of the oxides were studied by X-ray diffraction (XRD), four-probe direct current (DC) conductivity, environmental scanning electron microscopy (ESEM) and oxygen temperature-programmed desorption (O₂-TPD) technologies, respectively. At x = 0.0-0.15, BSCF had a cubic perovskite structure, the lattice parameter and electrical conductivity both decreased steadily with increasing A-site deficiency. The A-site deficiency resulted in the increasing oxygen vacancy concentration in the lattice structure and improved the sintering of the oxides. BSCF (x = 0.03) showed the highest oxygen permeability with the flux reaching 3.5 × 10^-6 mol cm^-2 s^-1 [STP: standard temperature and pressure] at 900 °C through a 1.0 mm thickness membrane. Long-term stability test of BSCF (x = 0.03) membrane at 850 °C indicated a slight deterioration of the permeation flux, which was attributed in part to the increased A-site deficiency of the bulk from Ba²⁺ and Sr²⁺ segregation over the membrane surface.