Investigation of the Proton Transport Mechanism in Sc-Doped CaZrO3 Using Ab-Initio Molecular Dynamics Simulations

Perovskite-based protonic conductors are promising electrolyte materials for solid oxide fuel cells. Although numerous studies have been conducted in these systems, many microscopic aspects related to proton transport are still unknown. We present ab initio molecular dynamics studies of proton transport in Sc-doped CaZrO3 to gain insights into proton conduction mechanisms. It is noted that the proton transfer along the two primary channels, namely, intraoctahedral and interoctahedral, is sensitive to the local cationic environments. While the proton hops in the Zr-O(H)-Zr environments are predominantly interoctahedral hops, the Zr-O(H)-Sc environments promote both channels alike. However, the interoctahedral proton hops from the Zr-O(H)-Sc environments are followed by persistent jump-reversals leading to the localization of the protons, with negligible contribution to the ionic conductivity. Exploiting the van-Hove correlation functions, it is demonstrated that the nature of the localization essentially involves proton scrambling over the ScO6 octahedra, unlike earlier perceptions. These results are complemented with proton binding energies and interoctahedral migration barriers, estimated respectively from geometry optimization and nudged elastic band calculations.