Crystal structure and oxygen permeation study of cobalt doped Sr4Fe6O13 mixed-conducting oxides

Mixed-conducting Sr4CoxFe6-xO13+/-delta oxides were synthesized by pyrolysis of cellulose-citric-metal salt compound. Their crystal structures were investigated, and oxygen permeability of Sr4Co2Fe4O13+/-delta was also studied by a GC method. The introduction of cobalt in Sr4Fe6O13 led to the occurrence of perovskite phase in the Sr4Fe6O13 bulk even at low doping content of cobalt (x=0.5), some minor CoO phase was also observed when x=2.0, and the material mainly demonstrated perovskite structure when x=2.6. The phase structure of Sr4COxFe6-xO13+/-delta was found to be closely related with the calcined temperature and the oxygen concentration in the ambient atmosphere during calcination or retreatment at high temperature. The air-synthesized sample had the intergrowth phase Sr4Fe6-xCoxO13+/-delta and the perovskite phase Sr(Fe, Co)O3-delta coexisted along with CoO impurity. The N-2-annealed sample coexisted of Sr4Fe6O13 phase, brownmillerite phase and minor CoO impuirty. When Sr4Co2Fe4O13+/-delta was treated in pure oxygen environment, the sample changed to single phase (Sr4Fe6O13 type phase). The oxygen permeability of Sr4Co2Fe4O13+/-delta membrane had a value close to 1.5x10(-8)mol/cm(2).s at 1123K. From 923K to 1223K, the activation energy for oxygen transportation was about 70kJ/mol.