Prediction of High Critical Temperature Superconductors in Ternary Y-Hf-H System under High Pressure

Achieving room-temperature superconductivity has been an enduring scientific quest, while hydrogen-rich compounds have emerged as highly promising candidates. Here, we systematically investigated the thermodynamic stability, crystal structure, electronic properties, and superconductivity within the ternary Y-Hf-H system under high pressure. Several distinct hydrides have been revealed, in which the hydrogen atoms are present in various hydrogenic motifs. A15-type hydride Pm\overline3-YHfH_6 with isolated H^- is predicted to be dynamically stabilized down to 10 GPa. The H atoms form pentagonal graphene-like layered-H_10 anions in the Hf plane of P\overline6-YHfH_19, with a T_\rm c of 95 K at 100 GPa. There are H cages in Cmmm-Y_3HfH_24, and attributed to the robust electron-phonon coupling and high electronic density of states of hydrogen at the Fermi level, it demonstrates near-room temperature superconductivity with a T_\rm c of 275 K at 250 GPa. Our work makes contributions to the understanding of the fundamental properties of ternary hydrides under high pressure and provides essential references for further research in this field.