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

Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing hydrogen. La_2-x-ySr_x+yLiH_1-x+yO_3-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 La_2-x-ySr_x+yLiH_1-x+yO_3-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.