High-temperature superconductivities and crucial factors influencing the stability of LaThH 12 under moderate pressures.

The recent discovery of high-temperature superconductivity in compressed hydrides has reignited the long-standing quest for room-temperature superconductors. However, the synthesis of superconducting hydrides under moderate pressure and the identification of crucial factors that affect their stability remain challenges. Here, we predicted the ternary clathrate phases of LaThH 12 with potential superconductivity under high pressures and specifically proposed a novel R 3̄ c -LaThH 12 phase exhibiting a remarkable T c of 54.95 K at only 30 GPa to address these confusions. Our first-principles studies show that the high- T c value of Pm 3̄ m and Cmmm -LaThH 12 phases was induced by the strong electron-phonon coupling driven by the synergy of the electron-phonon matrix element and phonon softening caused by Fermi surface nesting. Importantly, we demonstrate the dual effects of enhanced ionic bonding and expanded orbital hybridization between Th-6f and H-sp 3 orbitals during depressurization are primary factors governing the dynamic stability of R 3̄ c -LaThH 12 at low pressures. Our findings offer crucial insights into the underlying mechanisms governing low-pressure stability and provide guidance for experimental efforts aimed at realizing hydrogen-based superconductors with both low synthesis pressures and high- T c .