Designing Ambient Pressure Superconductivity in Li–Mg-Based Hydrides via Transition-Metal Modulation: From Quaternary to Quinary Systems

Hydrogen-rich superconductors have emerged as promising candidates for achieving high-temperature superconductivity, yet their practical applications are generally limited by the requirement for high external pressures. In this work, taking the Fm-3-XYZ2H12 structure as a prototype, we constructed a series of LiMgM2H12 quaternary hydrides and the LiMgZrHfH12 quinary hydride. High-throughput screening indicates that the three hydrides, LiMgZr2H12, LiMgHf2H12, and LiMgZrHfH12, are dynamically stable at ambient pressure but thermodynamically metastable. Electron–phonon coupling calculations show that the Tc values of LiMgZr2H12, LiMgHf2H12, and LiMgZrHfH12 reach 87.4, 81.2, and 85.2 K at ambient pressure, respectively, all exceeding the boiling point of liquid nitrogen and demonstrating excellent superconducting properties. Further analysis reveals that, compared with the Ga-based parent Fm-3-XYZ2H12 hydrides, Li substitution markedly reconstructs the electronic-state distribution near the Fermi level and enhances the contribution of H atoms to the density of states near the Fermi level. This promotes the coupling between conducting electrons and high-frequency hydrogen vibrations. Such strong electron–phonon coupling plays a crucial role in their high-temperature superconductivity. These findings provide valuable insights into the theoretical design of high-Tc superconductors under ambient pressure and offer theoretical guidance for future experimental studies in this field.