A novel Nb ₂O ₅-doped SrCo _0.8Fe _0.2O _3-δ oxide with high permeability and stability for oxygen separation

A new series of Nb ₂O ₅-doped (0.5, 1, 3, 5, 10 and 15wt.%) SrCo _0.8Fe _0.2O _3-δ (SCF) mixed conducting materials have been synthesized by the solid-state reaction method. The crystal structure, phase stability, oxygen desorption behavior, thermal expansion behavior, electrical conductivity and oxygen permeability of the prepared materials were systematically investigated. Doped Nb ₂O ₅ was completely incorporated into the SCF structure and effectively suppressed the coexisting orthorhombic phase in bulk cubic SCF and the perovskite-brownmillerite transition under low oxygen partial pressure. In situ high-temperature X-ray diffraction (HTXRD) also indicated good chemical and structure stability of the slightly doped Nb ₂O ₅ (0.5wt.%) at both 0.21×10 ⁵ and 1×10 ^-2Pa oxygen partial pressures at high temperatures. Nb ₂O ₅ dissolved into the SCF lattice served to some extent to decrease the electrical conductivity and oxygen flux, and increase the thermal expansion. The grain size of the membranes were significantly suppressed by the doping of Nb ₂O ₅. In particular, SCFNb0.5 with the cubic perovskite structure has the smallest cell parameters, the lowest thermal expansion and the highest oxygen flux.