Properties of Nb-doped SrCo0.8Fe0.2O3−d perovskites in oxidizing and reducing environments

The phase stability of SrCo_0.8Fe_0.2O_3−d perovskite doped with niobium was studied by in situ high-temperature X-ray diffraction in the temperature range of 30–1000 °C and oxygen partial pressure 0.2–10⁻⁵ atm. The stability of the cubic perovskite structure in a wide range of oxygen partial pressures is the main advantage of SrCo_0.8−xFe_0.2Nb_xO_3−d (x = 0.1–0.3) system in comparison with SrCo_0.8Fe_0.2O_3−d. It is suggested that equilibrium of the thermal expansion with changes of the oxygen non-stoichiometry leading to the same lattice parameters in the oxidizing and reducing environments at the catalytic temperatures is a necessary requirement for stable operation of perovskite as an oxygen-conducting membrane. In the case of SrCo_0.8−xFe_0.2Nb_xO_3−d perovskite this condition is met at x = 0.2. This makes the SrCo_0.6Fe_0.2Nb_0.2O_3−d composition promising for application as oxygen-conducting membrane.