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 oxides A 3 V 2 O 8 (A = Sr, Ba), which crystallize with a framework of isolated tetrahedral VO 4 units. We show that these systems present prevalent ionic conduction, with a large protonic component under humidified air ( t H ∼ 0.6-0.8) and high protonic mobility. In particular, the proton conductivity of Sr 3 V 2 O 8 is 1.0 × 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 facilitated by rotational motion of the VO 4 units, which can stabilize oxygen defects via formation of V 2 O 7 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.