Structure and oxygen permeability of BaCo0.7Fe0.3−xInxO3−δ ceramic membranes

BaCo0.7Fe0.3−xInxO3−δ (BCFI, x=0-0.20) materials, which are considered for application in oxygen separation technology, were prepared by conventional, solid-state reaction process. It was found that doping of indium in x=0.10-0.20 range stabilizes the cubic, perovskite-type structure at ambient temperature. Comprehensive studies were performed considering influence of indium content in BCFI oxides on electrical conductivity, oxygen nonstoichiometry, oxygen permeation behavior and structural stability of the materials. With increasing In content, oxygen vacancy concentration increases, while at the same time, electrical conductivity is found to decrease. Also, the oxygen permeability decreases with increasing In-doping level, which is due to the narrowing of the critical radius and the increasing of the activation energy of oxygen migration. This correlation was further elucidated by first principles calculations. From a point of view of application, incorporation of In enhances structural stability of the compounds in reducing atmospheres, and also, membranes with BaCo0.7Fe0.2In0.1O3−δ composition exhibited ability to recover the same crystal structure after reduction. For 1 mm thick membranes, a high oxygen permeation flux of about 1.48 mL cm−2 min−1 was measured at 900 °C under air/He gradient conditions.