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

Abstract

<div>Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing hydrogen. La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub> oxyhydride with a layered perovskite (K<sub>2</sub>NiF<sub>4</sub>-type) structure was discovered as a hydride ion conductor, and it was subsequently reported that Ba<sub>2</sub>ScHO<sub>3</sub> with the same crystal structure is also a hydride ion conductor. The two compounds have different anionic sites occupied by hydride ions. In La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub>, the hydride ions occupy equatorial anion sites, while the hydride ions are located at apical anion sites in Ba<sub>2</sub>ScHO<sub>3</sub>. This suggests that hydride ions diffuse through rock-salt layers in Ba<sub>2</sub>ScHO<sub>3</sub>. However, the specific diffusion mechanism resulting in ionic conductivity of Ba<sub>2</sub>ScHO<sub>3</sub> has not been clarified yet. In the present study, the point defect</div><div>formation energies and anionic conduction mechanisms of Ba<sub>2</sub>ScHO<sub>3</sub> were systematically analyzed using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in Ba<sub>2</sub>ScHO<sub>3</sub> 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.</div>