Yb Doping Effects on Structure and Performance of BaCo 0.7 Fe 0.3-x Yb x O 3-δ Perovskite

Abstract

Fe partial substitution for Co on B-site may tradeoff stability-activity for BaCoO3-delta perovskite. However, large radius mismatch between Ba and Co/Fe favors the formation of a low symmetric hexagonal phase BaCo1-xFexO3-delta, which may experience phase structural transitions with varying temperatures and could induce structural reliability issue of associated devices. The B-site doping with high valence elements may facilitate to form cubic BaCo1-xFexO3-delta perovskite, it could also significantly deteriorate their catalytic property. The Yb3+ with ionic radius being larger than those of Co4+ and Fe4+ could be used as B-site dopant to tune Goldschmidt tolerance factor of BaCo1-xFexO3-delta to 1 and therefore stabilize its cubic structure. Additionally, the electronegativity of Yb is lower than that of Co and Fe. This would induce a slightly lower valance of Co and/or Fe when Yb is used as B-site dopant, facilitating oxygen vacancy generation and electrochemical kinetic process. In this research, Yb-doping effects on crystal structure and performance of BaCo(0.7)Fe(0.3-x)YbxO(3-delta) (x = 0.05, 0.10 and 0.15) are systematically evaluated. The results indicate that Yb partial substitution for Fe on B-site is able to effectively stabilize crystal structure with highly cubic symmetry and BaCo0.7Fe0.2Yb0.1O3-delta is among the best as cathode material for intermediate temperature SOFCs.