High‐Temperature Superconductivity of Thermodynamically Stable Fluorite‐Type Hydrides at Ambient Pressure

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.