Mixed ionic-electronic conductors (MIECs) are essential for high-temperature electrochemical devices, such as solid oxide fuel cells and oxygen separation membranes. While it is difficult to optimize both ionic and electronic transport simultaneously in single-phase materials, composite systems offer a promising strategy by separating these functionalities into distinct and percolating phases. This study reports the functional properties of the nominal composition BaCe0.5Fe0.5O3 – δ (BCF), which forms a dual-phase composite due to the mismatch in ionic radii between the Ce4+ and Fe3+/4+ cations. The BCF material was synthesized via a single-step citrate-nitrate combustion route to ensure a homogeneous dual microstructure state consisting of an orthorhombic BaCeO3-based phase and a cubic BaFeO3-based phase. This was confirmed by Rietveld refinement and electron microscopy analyzes. Electrical characterization revealed moderate total conductivity at 300–750°C, which did not exceed 1 S cm–1. Despite its restricted electronic conductivity, the composite exhibited acceptable oxygen permeation fluxes, reaching 2.0 × 10–3 mL min–1 cm–2 at 750°C for a 650 µm-thick membrane. The calculated specific oxygen permeation flux exhibited thermally activated behavior with an activation energy (~0.75 eV) comparable to that of similar iron-containing perovskite systems. A comparative analysis with literature data showed that the BCF performance is acceptable for the 600–750°C range. These results highlight the effectiveness of the in situ formed composite, in which the Ce-rich phase facilitates ionic transport and compensates for the moderate electronic conductivity of the Fe-rich phase. Consequently, the BCF composite can be considered a promising material for oxygen transport membranes.
Кузнецова et al. (Sun,) studied this question.