Phase and microstructural characterizations for Ce_0.8Gd_0.2O_2-δ-FeCo₂O₄ dual phase oxygen transport membranes

Dual phase oxygen transport membranes were prepared via solid state reaction at 1200 ℃. The sintered membranes were characterized via X-ray diffraction, back scattered electron microscopy and electron backscatter diffraction, and associated with image analysis and calculations to quantify phase compositions and microstructural features including volume fractions, grain sizes, and contiguity. The characterizations reveal a multi-phase system containing Ce1-xGdxO2-δ’ (x ≈ 0.1) (CGO10), and FeyCo3-yO4 (0.2 < y < 1.2) (FCO), CoO and Gd0.85Ce0.15Fe0.75Co0.25O3 (GCFCO) in the sintered membranes. In addition, a novel model is utilized to assess the evolution of the ambipolar conductivity with respect to microstructural features. Both experimental and calculated results indicate that if the grain sizes of all phases in the composites are similar, the optimal ambipolar conductivity is reached with a volume ratio of ionic conducting phase to electronic conducting phase close to 4:1. Meanwhile, the GCFCO phase dominates the effective electronic conductivity.