Interest in oxide ion conducing materials has recently risen due to their application as electrolytes in solid oxide fuel cells (SOFCs) and solid oxide electrolysers cells (SOECs). Particular efforts are being made towards the development of materials that exhibit appropriate physical-chemical stability and good ionic conductivity at an intermediate temperature range (400 – 600 °C). Oxide ion conductivity has been reported in several structural families, demonstrating a strong correlation between the ionic transport and the crystal structure. We have recently identified significant oxide ion conductivity in the hexagonal perovskite derivative Ba3MoNbO8.5. This is the first example of a solid oxide ion conductor crystallising within the hexagonal perovskite class, thus unlocking a new direction in the research of oxide ion conductors. The Ba3MoNbO8.5 structure is a hybrid of the 9R hexagonal perovskite (9R) and palmierite (P) structures. (Mo/Nb)O4 and (Mo/Nb)O6 units coexist within the system, producing a disordered arrangement of tetrahedral and octahedral domains. Here we highlight the structural factors related to the oxide ion diffusion in Ba3MoNbO8.5. Neutron diffraction experiments and electrical characterisation of Ba3MoNbO8.5 and W-substituted compositions suggest how the relative number of tetrahedral to octahedral units affects the ionic conduction. The flexibility of the Ba3MoNbO8.5 crystal structure, where the Mo/Nb metal is able to swap between tetrahedral and octahedral coordination, is clearly a key factor for the significant oxygen mobility. We also show preliminary results on an analogous hexagonal perovskite compound, Ba7Nb4MoO20, which is also able to support oxide ion conductivity.

Oxide ion conductors in the hexagonal perovskite family

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.