High-Temperature Superconductivity in Li₂YH₆ Driven by Li Doping and a Specific Hydrogen-Cage Structure under High Pressures

Abstract

In this work, we predict that a new hydrogen-rich superconductor, Li₂YH₆, adopts a stable I4/mmm phase in the pressure range of 130–180 GPa, and is similar to YH₄ in terms of space-group symmetry and local hydrogen-environment features. Its maximum superconducting transition temperature (Tc) can attain 227 K at 150 GPa. At the microscopic level, Li acts as an electron donor and does not merely fill interstitial sites, but actively reconstructs the local hydrogen framework and its charge distribution, thereby inducing pronounced bonding heterogeneity characterized by the coexistence of H₂-like units and atom-like H. The synergistic effect of a specific stoichiometry and Li doping stabilizes this local hydrogen configuration. Such a structural feature not only preserves the hydrogen-dominated high-frequency vibrational characteristics, but also introduces additional Li-related intermediate-frequency coupling channels, thereby cooperatively optimizing the electron–phonon coupling and enhancing Tc. The incorporation of Li can also effectively reduce the metallization pressure of binary hydrides. A systematic comparison of the superconducting properties in the Li–Y–H system further shows that simply increasing the hydrogen content or forming a more hydrogen-rich cage-like framework does not necessarily guarantee a higher Tc. Instead, the superconducting response is jointly governed by factors related to "stoichiometry control", "hydrogen-network density", "bonding heterogeneity", and the “λ–⟨ω_log ⟩ trade-off”. These results provide a mechanism-oriented perspective for understanding ternary hydrogen-rich superconductors under high pressure, and may also offer useful inspiration for future candidate screening and machine-learning-assisted materials design.