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

<div>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</div><div>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.</div>

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

<div>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</div><div>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.</div>

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

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

The role of oxygen vacancies on the vibrational motions of hydride ions in the oxyhydride of barium titanate

Combined INS and DFT study on BaTiO3−xHx unravels the effect of oxygen vacancies on the vibrational dynamics of hydride ions.

Covalent Si–H Bonds in the Zintl Phase Hydride CaSiH1+x (x ≤ 1/3)

The crystal structure of the Zintl phase hydride CaSiH≈4/3 was discussed controversially, especially with respect to the nature of the silicon-hydrogen interaction. We have applied X-ray and neutron powder diffraction as well as total neutron scattering on a deuterated sample, CaSiD1.1. Rietveld refinement (CaSiD1.1, Pnma, a = 14.579(4) Å, b = 3.8119(4) Å, c = 11.209(2) Å) and an analysis of the neutron pair distribution function show a silicon-deuterium bond length of 1.53 Å. The Si–H bond may thus be categorized as covalent and the main structural features described by a limiting ionic formula Ca2+H−(Si−)2/3(SiH−)1/3. Hydrogen atoms decorating the ribbon-like silicon polyanion made of three connected zigzag chains are under-occupied, resulting in a composition CaSiH1.1. Hydrogen-poor Zintl phase hydrides CaSiH<1 with hydride ions in Ca4 tetrahedra only were found in an in situ neutron diffraction experiment at elevated temperature. Hydrogen (deuterium) uptake and release in CaSiDx (0.05 ≤ x ≤ 0.17) is a very fast process and takes less than 1 min to complete, which is of importance for possible hydrogen storage applications.