First-principles studies on the dynamic, mechanical and electronic properties of ZrCr₂H x (0 < x ≤ 4) under 0-20 Gpa

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 ≤ 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 at neighboring interstitials, 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 from H s orbital to the metallicity, suggesting that C15-type intermetallic hydrides have great potential to form high-temperature superconductors at low pressures.