Chemical reactivity of perovskite oxide SOFC cathodes and yttria stabilized zirconia

The chemical reactivity of perovskite oxide SOFC cathodes and yttria stabilized zirconia (YSZ) solid electrolyte was studied. The perovskite oxides that were examined were La1−xSrxCo0.2Mn0.8O3−d, La1−xSrxCo0.2Fe0.8O3−d and La1−xCaxCo0.2Fe0.8O3−d (0≤x≤0.5), as well as, the A-site deficient oxides La0.6−zSr0.4Co0.2Fe0.8O3−d, La0.6Sr0.4−zCo0.2Fe0.8O3−d and (La0.6Sr0.4)1−zCo0.2Fe0.8O3−d (0≤z≤0.2). Equimolar perovskite/YSZ powder mixtures were prepared and annealed at 1100°C for 120 h. X-ray diffraction analysis was conducted to identify any reaction products. Si-standard was used as an internal standard for d-value calibration, during the determination of the lattice parameter of cubic YSZ. The main reaction products were La2Zr2O7 for the undoped and lightly doped Fe-containing compositions and (Sr/Ca)ZrO3 for the Sr/Ca doped compositions. Also, CoFe2O4 was formed in the case of the Fe-containing compositions and monoclinic zirconia for La1−xCaxCo0.2Fe0.8O3−d with x=0.4, 0.5. A-site deficiency in La0.6Sr0.4Co0.2Fe0.8O3−d-based perovskites reduced the amount of SrZrO3 formed, only in the case of La0.6Sr0.4−zCo0.2Fe0.8O3−d with 0≤z≤0.2 and (La0.6Sr0.4)1−zCo0.2Fe0.8O3−d with z=0.2. The lattice parameter of YSZ exhibited a shift, corresponding to a lattice contraction, due to the diffusion of the transition metal cations from the perovskite into YSZ.