Correlation of structure, electrical conductivity, and oxygen permeability in strontium cobaltite ceramic membranes

An attempt has been made to synthesize a highly stable oxygen-deficient strontium cobaltite {SrCoO3-delta (delta = 5/16)} by decomposition of the sol-gel derived oxalate at 1000 degrees C for 10 h in air. The product corresponds to the rhombohedral Sr6Co5O15 (93 wt%) and spinel cubic Co3O4 (7 wt%) phases at room temperature but displays the perovskite-type cubic structure with a similar to 3.953 angstrom at 900 degrees C. It serves as an excellent material for separation of oxygen from the air and exhibits high oxygen permeability (J(O2)) of 3.0 ml/cm(2).min at 1000 degrees C for a 1.0 mm thick membrane. The activation energy of the process is found as 22 kJ/mol. Further, both J(O2) and conductivity (sigma) reveal good correlation with phases present at different temperatures. The system shows (i) reversible phase separation following the reaction SrCoO3-delta -> Sr6Co5O15 + Co3O4 and (ii) hysteresis in oxygen permeability upon cooling but remains reusable.