Abstract
Hydride superconductors have attracted significant attention, yet achieving superconductivity at ambient pressure remains a key challenge. Here, a family of high-T(c) (superconducting critical temperature, T(c)) hydrides based on the fluorite-type AXH(8) structure, exhibiting thermodynamic and dynamic stability at low to atmospheric pressure, is proposed. Through comprehensive screening of 150 ternary systems, eight stable hydrides below 35 GPa are identified. Notably, AcRhH(8) and BaRhH(8) show ambient-pressure stability, while AcIrH(8) and BaIrH(8) are stable at 3 GPa, demonstrating great potential for practical applications. Several compounds surpass the liquid-nitrogen T(c) threshold, including AcRhH(8) (78 K at 0 GPa), LaRhH(8) (94 K at 24 GPa), LaOsH(8) (83 K at 35 GPa), and CeOsH(8) (106 K at 31 GPa). Mechanistic analysis reveals that large-radius A-site atoms serve as electron donors, stabilizing the framework and promoting weak covalent connections among [XH(8)](n-) anionic units. This leads to a 3D weak covalent network that enhances electron delocalization, increases the density of states at the Fermi level, and strengthens electron-phonon (EPC). Moreover, a linear correlation between minimum ELF at H(8) tetrahedral connections and EPC constant further highlights the role of hydrogen-framework charge delocalization in boosting superconductivity.