Strain-induced tunable energy barrier of proton diffusion in Y-doped BaCeO₃ and Y-doped BaZrO₃

In this paper, the strain effects on the energy barrier of proton diffusion in Y-doped BaCeO₃ (BCY) and Y-doped BaZrO₃ (BZY) are investigated by detailed density functional theory calculations. The energy barrier of proton rotation decreases when the tensile strain is applied. For intra-octahedral proton transfer, the energy barrier decreases when the tensile strain is applied while for inter-octahedral proton transfer the energy barrier increases when the tensile strain is applied. However, we found that for intra-octahedral proton transfer the energy barrier of BZY shows the opposite strain effect. To understand the underlying mechanism behind this opposite trend we decomposed proton diffusion into three elementary steps and the opposite trend of the energy barrier of BCY and BZY during intra-octahedral proton transfer is pinpointed to the opposite bond order change of the hydrogen bond. In all, we explored the strain effects on the energy barrier of proton diffusion in BCY and BZY from a microscopic perspective, showing the potential to tune the energy barrier of proton transport in perovskite oxide with strain engineering and thus design novel proton conductors.