Preparation and oxygen permeation properties of La_0.7Sr _0.3Co_0.2Fe_0.8O_3-δ membrane

La_0.7Sr_0.3Co_0.2Fe_0.8O _3-δ oxide was synthesized by a citrate method and a typical dense membrane of perovskite oxide has been prepared using as-prepared powder by pressing and sintering at 1300 °C. Precursor of La_0.7Sr _0.3Co_0.2Fe_0.8O_3-δ prepared by citrate method was investigated by TGA and XRD. Metal-citrate complex in precursor was decomposed into perovskite oxide in the temperature range of 260-410 °C but XRD results showed SrCO₃ existed as impurity at less than 900 °C. Electrical conductivity of membrane increased with increasing temperature but then decreased over 700 °C in air atmosphere (Po₂ = 0.2 atm) and 600 °C in He atmosphere (Po₂ = 0.01 atm) respectively due to oxygen loss from the crystal lattice. The oxygen permeation flux increased with increasing temperature and maximum oxygen permeation flux of La_0.7Sr_0.3Co_0.2Fe _0.8O_3-δ membrane with 1.6 mm thickness was about 0.31 cm³/cm² · min at 950 °C. The activation energy for oxygen permeation was 88.4 kJ/mol in the temperature range of 750-950 °C. Perovskite structure of membrane was not changed after permeation test of 40 h and the membrane was stable without secondary phase change with 0.3 mol Sr addition.