Layered Perovskites BaM₂In₂O₇ (M = La, Nd): From the Structure to the Ionic (O^2-, H⁺) Conductivity

The design of new oxide compounds that can be used as oxygen- or proton-conducting electrolytes for solid oxide fuel cells is actively in progress. Despite the intensive research activities regarding electrolytes with perovskite/fluorite structures, the search for other structural alternatives is of paramount importance. In this study we focus on a novel material with significantly improved properties for the electrochemical purposes. The two-layered BaNd₂In₂O₇ perovskite with a Ruddlesden-Popper structure was investigated as a protonic conductor for the first time. In detail, its local structure, water uptake, and the ionic (O^2-, H⁺) conductivity were comprehensively studied. The nature of rare-earth elements (M = La, Nd) in the structure of BaM₂In₂O₇ on the structural and transport properties was revealed. The presented analysis showed that the composition of BaNd₂In₂O₇ is nearly pure proton conductor below 350 °C. This work opens up a new way in the design of protonic conductors with double-layered perovskite structure.