The mixed-conducting perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), given its outstanding oxygen ionic and electronic transport properties, is considered a promising material composition for oxygen transport membranes (OTM) operated at high temperatures.
Its long-term stability under operating conditions is, however, still an important issue. Although the incompatibility of BSCF with CO2-containing atmospheres can be avoided by appropriate means (oxyfuel processes in the absence of carbon dioxide), the thermal as well as the chemical stability of BSCF itself are still under thorough investigation.
This work is focused on the stability of BSCF in the targeted temperature range for OTM applications (700…900 °C) and in atmospheres with low oxygen contents. Previous studies in literature suggest limited chemical stability below oxygen partial pressures pO2 of around 10-6 bar.
By using a coulometric titration method based on a zirconia “oxygen pump” setup, precise control of the oxygen partial pressure pO2 between 1 bar and 10-18 bar was facilitated. Combining electrical measurements on dense ceramic bulk samples performed as a function of pO2 with an XRD phase composition study of single phase BSCF powders subjected to various pO2 treatments, an assessment of the chemical stability of BSCF is facilitated as a function of oxygen partial pressure. It could thus be shown that the pO2 stability limit is considerably lower than previously assumed in literature.