A novel Nb2O5-doped SrCo0.8Fe0.2O3−δ oxide with high permeability and stability for oxygen separation

A new series of Nb2O5-doped (0.5, 1, 3, 5, 10 and 15 wt.%) SrCo0.8Fe0.2O3−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 Nb2O5 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 Nb2O5 (0.5 wt.%) at both 0.21 × 105 and 1 × 10−2 Pa oxygen partial pressures at high temperatures. Nb2O5 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 Nb2O5. In particular, SCFNb0.5 with the cubic perovskite structure has the smallest cell parameters, the lowest thermal expansion and the highest oxygen flux.