First-Principles Calculations of Point Defect Formation and Anion Diffusion Mechanism in Oxyhydride Ba2ScHO3

Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing
hydrogen. La2-x-ySrx+yLiH1-x+yO3-y oxyhydride with a layered perovskite (K2NiF4-type) structure was
discovered as a hydride ion conductor, and it was subsequently reported that Ba2ScHO3 with the same
crystal structure is also a hydride ion conductor. The two compounds have different anionic sites
occupied by hydride ions. In La2-x-ySrx+yLiH1-x+yO3-y, the hydride ions occupy equatorial anion sites,
while the hydride ions are located at apical anion sites in Ba2ScHO3. This suggests that hydride ions
diffuse through rock-salt layers in Ba2ScHO3. However, the specific diffusion mechanism resulting in
ionic conductivity of Ba2ScHO3 has not been clarified yet. In the present study, the point defect
formation energies and anionic conduction mechanisms of Ba2ScHO3 were systematically analyzed
using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in
Ba2ScHO3 rather than oxide ions. The migration energies of vacancy, interstitial and interstitialcy
mechanisms were evaluated, and the activation energies of hydride ionic diffusion mediated by the
vacancy and the interstitialcy processes was found to be the lowest.