High-temperature superconductivity of ternary Y–Hf–H compounds under high pressure

Compressed ternary alloy superhydrides are currently considered to be the most promising competitors for high-temperature superconducting materials. Here, the stable stoichiometries in the Y-Hf-H ternary system under pressure are comprehensively explored and four fresh phases are found: Pmna -YHfH ₆ and _{P 4/ mmm -YHfH 7 at 200 GPa, P 4/ mmm -YHfH 8 at 300 GPa and P -6 m 2-YHfH 18 at 400 GPa. The four Y-Hf-H ternary phases are thermodynamically and dynamically stable at corresponding pressure. In addition, structural features, bonding characteristics, electronic properties, and superconductivity of the four ternary Y-Hf-H phases are systematically calculated and discussed. Among them, the superconducting transition temperatures ( T c ) are significantly enhanced as the hydrogen content and the contribution of H atoms to the density of states at the Fermi level increase. The P -6 m 2-YHfH 18 with high hydrogen content exhibits a high T c value of 130 K at 400 GPa.}