Suppress Oxygen Ordering and Deviation for the Design of Bismuth Oxide-based Low Temperature Ionic Conductors

Bismuth oxide shows promise for oxygen ion conduction, with its high-temperature δ phase exhibiting exceptional conductivity over state-of-the-art conductors. The δ phase can be stabilized through doping, yet the stabilized phases suffer from severe conductivity decay at lowered temperatures with unclear oxygen sublattice transitions and orderings. Here, we identify the ground-state phase of δ-Bi2O3 featuring oxygen ions deviated to the 48g sites of its fluorite structure, exhibiting the lowest energy among all derivative structures. Our prediction is then confirmed through direct characterization of the oxygen positions with high-resolution electron microscopy. Using molecular dynamics, we further reveal the decay mechanism of oxygen ion transport upon cooling, which arises from the occupation of 48g sites and concurrent oxygen sublattice ordering. Armed with this knowledge, we conduct a screening of metal dopants for anionic deviation and ordering suppression. Our candidates will improve the oxygen ionic conductivity of δ-Bi2O3-based conductors for low temperature operations.