Structure and oxygen permeability of BaCo_0.4Fe _0.6-xZr_xO_3-δ oxide: Effect of the synthesis method

The structure and oxygen permeability of BaCo_0.4Fe _0.6-xZr_xO_3-δ prepared by the solid-state reaction (SSR) method and the modified citrate (MC) method were compared. X-ray diffraction revealed that, for the calcined powders prepared by the SSR method, BaZrO₃, besides the major perovskite phase, was detected, while the single perovskite phase with a cubic structure was found over the entire composition range for the powders synthesized by the MC method. The lattice parameter of BaCo_0.4Fe_0.6-xZr_xO _3-δ prepared by the MC method was larger than that prepared by the SSR method at the same Zr content, which was attributed to the different amounts of Zr dissolved in the BaCoFeO lattice resulting from various synthesis methods. Thermogravimetry-differential scanning calorimetry thermal analysis indicated the different reaction mechanisms involved in the two methods. BaCo_0.4Fe_0.6-xZr_xO_3-δ prepared by the MC method showed remarkable structural stability when x ≥ 0. 2 in a atmosphere containing H₂, while all of the samples prepared by the SSR method changed their structure under a reducing atmosphere. The oxygen permeabilities of the membranes synthesized by the SSR method were slightly higher than those synthesized by the MC method. The difference in structural stability and oxygen permeability was thought to be caused by the different amounts of Zr dissolution in the perovskite phase resulting from different preparation methods.