关键词: metal hydrides, proton diffusion, superionic, first-principles study

Abstract: Ternary metal hydrides play a vital role in the search for conventional high-temperature superconductors under near-ambient pressures. In this study, we examine the dynamic, mechanical, and electronic properties of the C15-type ZrCr$_{2}$H$_{x}$ ($0 < x \le 4$) compounds at 0-20 GPa using first-principles simulations. We find that protons diffuse predominantly {via} the interstitial network composed of $g$ and $e$ sites, avoiding high-barrier $b$ sites. Proton diffusion is insignificant at 300 K, but increases markedly with increasing temperature, leading to superionic transitions at 900 K in all these hydrides. Diffusion enhances the occupation probability of neighboring interstitial sites, resulting in short H-H separations that violate the Switendick criterion. The calculated thermoelastic properties indicate mechanical stability of ZrCr$_{2}$H$_{x}$ at room temperature. In ZrCr$_{2}$H$_{4}$, the high hydrogen concentration leads to a clear contribution of H $s$ orbitals to metallicity, suggesting that C15-type intermetallic hydrides have great potential to form high-temperature superconductors at low pressures.

Key words: metal hydrides, proton diffusion, superionic, first-principles study