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 ZrCr₂H_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 of neighboring interstitial sites, resulting in short H–H separations that violate the Switendick criterion. The calculated thermoelastic properties indicate mechanical stability of ZrCr₂H_x at room temperature. In ZrCr₂H₄, 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.