The Mystery behind Dynamic Charge Disproportionation in BaBiO3

BaBiO3(BBO) is known to be a valence-skipping perovskite, which avoids the metallic state through charge disproportionation (CD), the mechanism of which is still unresolved. A novel mechanism for CD is presented here in the covalent limit using a molecular orbital (MO) picture under two scenarios: (case i) Bi 6sp-O 2p and (case ii) Bi 6p-O 2p hybridizations that favor 5+ and 3+ states, respectively. The proposed model is further validated by using a combinatorial approach of X-ray spectroscopic experiments and first-principle calculations. The bulk X-ray photoemission spectrum reveals that, at room temperature, the CD is dynamic in nature, whereas, at 200 K, it approaches a quasi-static limit. Under compressive strain, the octahedral breathing mode is damped and drives the system to a quasi-static limit even at room temperature, giving rise to asymmetric CD.

Automated summary

This study investigates the mechanism of charge disproportionation in BaBiO3, finding that different hybridizations lead to different oxidation states in the material, validated through a combination of X-ray spectroscopic experiments and first-principle calculations. Additionally, the nature of charge disproportionation varies at room temperature and 200K.