Pressure-driven charge transfer and tunable superconductivity in intermetallic Li–Mg electrides

Electrides, materials in which a portion of valence electrons reside as interstitial anionic electrons (IAEs) within lattice cavities—exhibit a wide range of extraordinary physical and chemical properties, making them a central focus of condensed matter physics. Under high pressure, intermetallic systems provide a unique pathway to novel electrides by enabling unconventional charge-transfer mechanisms. Here, we employ first-principles structure searches to identify two stable Li-Mg electrides, Li 3 Mg and Li 4 Mg. At low pressure, Mg atoms act as anionic centers through occupation of their outer-shell 3 p orbitals. Upon compression, charge is transferred from Mg to the lattice cavities, enhancing the localization and density of IAEs. This, in turn, strengths electron–phonon coupling and raises the superconducting transition temperature ( T c ) to 13.3 K at 75 GPa for Li 3 Mg and 19.7 K at 80 GPa for Li 4 Mg—values that surpass most known electride superconductors below 100 GPa. Selective hydrogen insertion into the lattice cavities in Li 4 Mg quenches the IAEs and confirms their essential role in superconductivity. Further compression drives a transition to poor or non-superconducting phases, with Mg atoms switching from electron acceptors to donors, contrary to the typical behavior of electropositive metals, which tend to transition from donors into acceptors under pressure. These findings highlight the pivotal role of IAEs in electride superconductivity and pave the way for designing novel intermetallic electrides with tunable properties. • Discovery of two previously unreported Li–Mg intermetallic electrides featuring Mg-centered anionic frameworks. • Evidence that pressure-induced charge transfer modulates both electron–phonon coupling and superconducting T c . • Computational demonstration of the indispensable role of interstitial electrons via hydrogen insertion. • Pressure reversers Mg’s role from acceptor to donor, offering a new paradigm for designing tunable superconductors.