Oxygen transport properties and stability of mixed-conducting ZrO₂-promoted SrCo_0.4Fe_0.6O_3-δ oxides

The oxygen nonstoichiometry, transport properties, and structure stability of ZrO₂-promoted SrCo_0.4Fe_0.6O_3-δ (SCFZ) were investigated. The nonstoichiometry of SCFZ increased with increasing temperatures and decreasing oxygen partial pressures. The results of X-ray diffraction and oxygen desorption experiments showed that the addition of ZrO₂ in SrCo_0.4Fe_0.6O_3-δ (SCF) stabilized the phase structure under low oxygen partial pressure. The chemical diffusion coefficient of oxygen in SCFZ in a temperature range of 928-1178 K was obtained using the weight relaxation technique. A simple transport equation correlating oxygen flux to the oxygen diffusion coefficient was deduced. Model calculations, based on the transport equation in conjunction with data of oxygen permeation and oxygen nonstoichiometry, were performed. The rates of oxygen permeation fluxes measured at various temperatures and time showed that the long-term operation stability of the SCF membrane with the addition of ZrO₂ was greatly improved. The oxygen permeation flux, however, was slightly reduced.