Mechanism of Hydride-Ion Diffusion in the Oxyhydride of Barium Titanate

Perovskite-type oxyhydrides stand out as hydride-ion conductors of relevance for diverse technological applications, but fundamental questions surrounding the relationship between the mechanism of hydride-ion diffusion and the local structure of these materials remain to be elucidated. Here, in a quasielastic neutron scattering (QENS) study of two perovskite-type oxyhydrides of barium titanate, BaTiO2.67H0.12□0.21 (□ refers to anion vacancies) and BaTiO2.88H0.12, we establish that the mechanism of hydride-ion diffusivity relies on hydride-ion jumps to nearest-neighbor anion vacancies. Combined analyses of QENS and structural data for BaTiO2.67H0.12□0.21 show that the diffusion process is characterized by two different time scales, possibly related to diffusion in regions featured by different concentrations of anion vacancies. It follows that designing materials with specific concentrations of anion vacancies may be an effective route to optimize hydride-ion conductivity toward specific applications.