Micromechanical Characterization of Ce_0.8Gd_0.2O_2-δ–FeCo₂O₄ Dual Phase Oxygen Transport Membranes

Aiming toward an optimization of dual phase oxygen transport membrane materials for oxygen separation applications, ceramic composites consisting of a Ce_1−xGd_xO_2−δ (0 < x < 0.2) fluorite phase, Gd_0.9Ce_0.1Fe_0.8Co_0.2O₃ perovskite phase, Fe_xCo_3−xO₄ (0 < x < 1) spinel phase, and CoO rock salt phase are developed and micromechanical properties (elastic modulus and hardness) of xCe_0.8Gd_0.2O_2−δ: (1−x)FeCo₂O₄ (50 wt% ≤ x ≤ 90 wt%) composites are characterized via indentation testing at room temperature. The results obtained at low indentation loads indicate that the magnitude of the elastic moduli of the different phases is in the order Gd_0.9Ce_0.1Fe_0.8Co_0.2O₃ > Ce_1−xGd_xO_2−δ ≈ Fe_xCo_3−xO₄ > CoO, and furthermore, hardness values are also in the same order. The hardness values of the obtained composites at higher impression loads reveal a stronger dependency on porosity than on composition due to similar hardness values of the main phases. Any compositional effect appears to diminish above a porosity of ≈1%.