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 into the thermodynamic stability, crystal structure, electronic property, 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 Pm3̅-YHfH₆ with isolated H^- is predicted to be dynamically stabilized down to 10 GPa. The H atoms form pentagonal graphene-like layered-H₁₀ anions in the Hf plane of P6̅-YHfH₁₉, with a T_c of 95 K at 100 GPa. There are H cages in Cmmm-Y₃HfH₂₄, 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_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.