Structural Evolution, Dual Role of Hydrogen and Superconductivity in Lithium-Rich Li-N-H Compounds under High Pressure

Using first-principles calculations combined with CALYPSO structure prediction method, we systematically investigated the crystal structures, electronic properties, and superconducting behavior of the Li-N-H ternary system under pressure ranging from 100 to 300 GPa. Six thermodynamically stable or metastable Li-rich compounds were identified: C2 Li₂NH, P2₁2₁2₁ Li₂NH, I4/mmm Li₃NH, Imm2 Li₈NH, Cm Li₉NH, and P2/c Li₁₀NH. The results reveal a distinct evolution in the chemical role of hydrogen with increasing lithium content. In phases with lower Li content, H atoms tend to form covalent bonds with N atoms, thereby achieving a stable closed-shell electronic configuration. As the Li content increases, H atoms progressively occupy lattice interstitial sites, acting as electron acceptors that trap excess interstitial anionic electrons (IAEs). This transformation effectively tunes the quantity, degree of localization, and spatial topology of IAEs. Correspondingly, C2 Li₂NH, P2₁2₁2₁ Li₂NH, and I4/mmm Li₃NH are insulating non-electrides, while Imm2 Li₈NH, Cm Li₉NH, and P2/c Li₁₀NH are electrides, which exhibit metallic behavior. Notably, P2/c Li₁₀NH demonstrates superconductivity with a predicted transition temperature of 4.8 K at 100 GPa, mainly originating from the strong electron-phonon coupling between H-p orbital electrons and low frequency phonon modes dominated by Li atoms. This work elucidates the dual functional role of hydrogen in high-pressure Li-N-H systems—from covalent N―H bonding coordination to IAEs capturing—and provides theoretical insights for the rational design of novel high-pressure electrides and superconducting materials.