Stabilization of the perovskite structure in Co-based mixed conductors by tri-valent cation substitution
Abstract For Co-based perovskite mixed conductors, the substitution of Co by cations with a higher valence than Co has been known to be effective in stabilizing the cubic perovskite structure. Nevertheless, such a substitution may reduce the number of the oxygen vacancies and be unfavorable for increasing oxygen permeability. In order to prepare cubic perovskite mixed conductors with greater oxygen permeability, the effect of substituting the tri-valent cation, In3 +, in the Co-based system (Ba,Sr)(Co,In)O3-δ, was investigated and compared to the effect of substituting Y, Al, and Fe. For (BaxSr1-x)(Co0.9In0.1)O3 − δ and (BaxSr1 − x)(Co0.9Y0.1)O3 − δ, cubic perovskite single phase was found to be attained at high Ba concentrations of x = 0.9 and 1.0 ≥ x ≥ 0.5. This differed from the cases of (BaxSr1 − x)(Co0.9Al0.1)O3 − δ and (BaxSr1 − x)(Co0.9Fe0.1)O3 − δ in which pure perovskite appeared in the low Ba concentration ranges of 0.2 ≥ x ≥ 0 and 0.5 ≥ x ≥ 0, respectively. A disk sample of (Ba0.9Sr0.1)(Co0.9In0.1)O3 − δ with 1 mm thickness showed high oxygen permeability of 5.69 cm3/min/cm2 at 900 °C, which was 24% higher than the permeability of (Ba0.5Sr0.5)(Co0.8Fe0.2)O3 − δ.