Abstract: Mixed-conducting Sr₄Co_xFe_6-xO_13±δ oxides were synthesized by pyrolysis of cellulose-citric-metal salt compound.
Their crystal structures were investigated, and oxygen permeability of Sr₄Co₂Fe₄O_13±δ 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 Sr₄Co_xFe_6-xO_13±δ 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 Sr₄Fe_6-xCo_xO_13±δ and the perovskite phase Sr(Fe, Co)O_3-δ coexisted along with CoO impurity. The
N₂-annealed sample coexisted of Sr₄Fe₆O₁₃ phase, brownmillerite phase and minor CoO impuirty. When Sr₄Co₂Fe₄O_13±δ
was treated in pure oxygen environment, the sample changed to single phase (Sr₄Fe₆O₁₃ type phase). The oxygen permeability of
Sr₄Co₂Fe₄O_13±δ membrane had a value close to 1.5×10^-8mol/cm²·s at 1123K. From 923K to 1223K, the activation energy for oxygen transportation was about 70kJ/mol.

Key words: mixed-conducting oxide, cellulose, Sr₄Co_xFe_6-xO_13±δ, phase structure, oxygen separation