The spin-state effect on the redox performance of LaCoO3 perovskites

Abstract

LaCoO3 is well-known for its unique thermally induced transition of Co3+ (3d6) ions from a low spin (LS) state to a higher spin state of intermediate spin (IS) state or high spin (HS) state, due to a delicate balance between crystal-field splitting and Hund’s coupling. In this work, we try to stabilize all possible spin states in the same initial structural model and further investigate the spin-state effect on the redox performance of LaCoO3. We find that an initial model of pseudocubic with R3¯c tilting octahedra was effective in stabilizing all possible spin states. The oxygen vacancy formation values of LS > HS + LS > HS > IS indicate that the IS state is the most optimal spin state in oxygen vacancy formation, which results from a weakened Co-O bonding energy by eg orbital occupation. The oxygen migration barriers of LS > IS > HS + LS > HS show that oxygen migration is easier in the relatively loose structure and thus LS structure is the most unfavorable in oxygen migration. Combining the oxygen vacancy formation and migration results, we conclude that the higher spin states of IS and HS are more beneficial than LS in oxygen conduction. Our results confirm the influence of the spin-state effect on oxygen conduction and show that spin-state regulation is a good strategy for improving the redox performance of perovskites.