Study of phase stability and hydride diffusion mechanism of BaTiO ₃ oxyhydride from first-principles

First-principles calculations were performed to study structural, electronic and hydride diffusion properties of BaTiO₃ oxyhydride. In agreement with experiment (Nat. Mater. 2012, 11, 507 and J. Am. Chem. Soc. 2012, 134, 8782), we find that the incoming H species occupy the anion vacancy sites left by oxygen, forming the stable hydride anions H^-1. As a result of the electron doping introduced by H species, both interstitial H and hydride anion H^-1 can induce metallicity and eliminate ferroelectricity in BaTiO₃. We further clarify the role of the migration of the interstitial H in determining the hydrogen diffusion properties of the oxyhydrides. A low diffusion barrier was predicted, responsible for high hydrogen diffusion mobility observed in experiment. Based on our results, we demonstrate that BaTiO₃ oxyhydride can be used as a mixed electron/hydride conductor, displaying the promising applications as the electrolytes for solid-oxide fuel cells.