Proton and Oxide Ion Conductivity in Palmierite Oxides

Solid proton and oxide ion conductors have key applications in several hydrogen-based and energy related technologies. Here we report on the discovery of significant proton and oxide ion conductivity in palmierite ox-ides A3V2O8 (A = Sr, Ba), which crystallize with a framework of isolated tetrahedral VO4 units. We show that these systems present prevalent ionic conduction, with a large protonic component under humidified air (tH = 0.6 – 0.8) and high protonic mobility. In particular, the proton conductivity of Sr3V2O8 is 1.0 x 10-4 S cm-1 at 600 °C, competitive with the best proton conductors constituted by isolated tetrahedral units. Simulations show that the three-dimensional ionic transport is vacancy driven and is facilitated by rotational motion of the VO4 units, which can stabilize oxygen defects via formation of V2O7 dimers. Our findings demonstrate that palmierite oxides are a new promising class of ionic conductors where stabilization of parallel vacancy and interstitial defects can enable high ionic conductivity.