Ternary Superconducting Hydrides TbNaH₁₂ and Its Hydrogen Sublattice Symmetry Effect on Superconducting Critical Temperature

Currently, hydrogen-rich compounds with hydrogen clathrate structures (e.g., CaH6, LaH10) are considered the most promising high-temperature superconducting materials under pressure. The quest for superconductors among clathrate hydrides has recently shift focus toward ternary hydrides. Herein, we proposed a new ternary superconducting hydrides TbNaH12 at 200 GPa and identified its stable Fd3¯m phase and metastable Pm3¯m phase. Interestingly, the H-sublattices in these two phases form H24 cage structures similar to those in CaH6, but their H24 cages consist of inequilateral H4 and H6 rings, showing different H-sublattice symmetries. Compared to the low-symmetry H-sublattices in Fd3¯m, the high-symmetry H-sublattices in Pm3¯m contribute more significantly to the Fermi level, bringing a strong electron–phonon coupling and further causing a high superconducting critical temperature (Tc). Pm3¯m was predicted to host a Tc of up to 208 K at 200 GPa, which is markedly higher than that of Fd3¯m (Tc ∼ 150 K) and even close to that of CaH6 (Tc ∼ 212 K). This will not only raise new ternary superconducting hydrides template but also reveal the effect of H-sublattices symmetry for Tc in superconducting hydrides.