Ternary Superconducting\nHydrides TbNaH<sub>12</sub> and Its Hydrogen\nSublattice Symmetry Effect on Superconducting Critical\nTemperature

Currently, hydrogen-rich compounds\nwith hydrogen clathrate structures\n(e.g., CaH<sub>6</sub>, LaH<sub>10</sub>) are considered the most\npromising high-temperature superconducting materials under pressure.\nThe quest for superconductors among clathrate hydrides has recently\nshift focus toward ternary hydrides. Herein, we proposed a new ternary\nsuperconducting hydrides TbNaH<sub>12</sub> at 200 GPa and identified\nits stable <i>Fd</i>3̅<i>m</i> phase and metastable <i>Pm</i>3̅<i>m</i> phase.\nInterestingly,\nthe H-sublattices in these two phases form H<sub>24</sub> cage structures\nsimilar to those in CaH<sub>6</sub>, but their H<sub>24</sub> cages\nconsist of inequilateral H<sub>4</sub> and H<sub>6</sub> rings, showing\ndifferent H-sublattice symmetries. Compared to the low-symmetry H-sublattices\nin <i>Fd</i>3̅<i>m</i>, the high-symmetry H-sublattices\nin <i>Pm</i>3̅<i>m</i> contribute more significantly\nto the Fermi level, bringing a strong electron–phonon coupling\nand further causing a high superconducting critical temperature (<i>T</i><sub>c</sub>). <i>Pm</i>3̅<i>m</i> was predicted to host\na <i>T</i><sub>c</sub> of up to 208 K at 200 GPa, which\nis markedly higher than that of <i>Fd</i>3̅<i>m</i> (<i>T</i><sub>c</sub> ∼ 150 K) and even close to that of CaH<sub>6</sub> (<i>T</i><sub>c</sub> ∼ 212 K). This will not only\nraise new ternary superconducting hydrides template but also reveal\nthe effect of H-sublattices symmetry for <i>T</i><sub><i>c</i></sub> in superconducting hydrides.