Preparation and transport properties of Ba3Nb2O8 hexagonal perovskite-derivative oxide

Hexagonal perovskite-derivatives attract increasing attention due to their high oxide ion conductivity at high temperature. In this work, pristine Ba₃Nb₂O₈ was chosen as the research target, since this composition is the cornerstone for some fast oxide ion conductors like Ba₃MoNbO_8.5. The knowledge on preparation and transport properties of Ba₃Nb₂O₈ is thereby valuable to the further design of excellent oxide ion conductors. The parameters for the solid-state reaction method to prepare a Ba₃Nb₂O₈ single phase were studied, and the optimal temperature and time for sintering were found to be 1200 °C and 36–48 h, respectively. By exposing to a humid atmosphere, Ba₃Nb₂O₈ can be hydrated to activate proton conduction, which is evidenced by higher bulk conductivity in the wet atmosphere and observation of H₂O/D₂O isotope. The transport number of proton conduction is further determined by electromotive force measurements to be around 0.6 at 500 °C and decreases with the increasing temperature.