Theoretical Investigation of Proton Diffusion in Dion-Jacobson Layered Perovskite RbBiNb₂O₇

Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb₂O₇ is a double-layered Dion-Jacobson perovskite oxide, with Pmc2₁ symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb₂O₇ were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb₂O₇ plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb₂O₇ were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb₂O₇ presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb₂O₇ exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO₃, CaZrO₃, and SrZrO₃. The proton diffusion in the Rb-O and Nb-O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb₂O₇ would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion-Jacobson structured RbBiNb₂O₇, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).