Intra-octahedral proton transfer in bulk orthorhombic perovskite barium cerate

Intra-octahedral proton transfer in bulk orthorhombic perovskite barium cerate was investigated in order to understand the proton transfer mechanism using density functional theory. Since Ce-centered octahedrons tilt in the orthorhombic perovskite structure to accommodate the tensile strain between Ba and O ions, the CeOCe unit is bent. A proton attached to an O ion can transfer intra-octahedrally to a neighboring O ion in the structure. An energy barrier of 1.06 eV is required as the bent CeOCe unit is straightened and bent in the opposite direction during proton transfer. When the bent CeOCe unit rotates without being straightened during proton transfer, a much lower energy barrier of 0.26 eV is required. The energy barrier for proton transfer by rotating the bent CeOCe unit increases to 0.45 eV, when the proton transfers near a Y ion that is substituted for a Zr ion as a dopant. Therefore, the proton transfers by rotating the bent CeOCe unit in bulk orthorhombic barium cerate, resulting in better agreement with experimentally measured energy barriers (0.5–0.54 eV).