Lithium-bismuth compounds with superconducting and superionic states at high pressure

Lithium-rich compounds offer exciting opportunities to explore novel high-pressure phenomena, with their structural, electronic, superconducting, and superionic behaviors attracting increasing attention. Here, using crystal structure prediction and first-principles calculations, we identify three stable Li-Bi compounds at high pressure, including $Fm\text{\ensuremath{-}}3m$ ${\mathrm{Li}}₃\mathrm{Bi}$, $R\text{\ensuremath{-}}3m$ ${\mathrm{Li}}₄\mathrm{Bi}$, and $P6/mmm$ ${\mathrm{Li}}₅\mathrm{Bi}$. Notably, ${\mathrm{Li}}₄\mathrm{Bi}$ and ${\mathrm{Li}}₅\mathrm{Bi}$ are identified as electrides, exhibiting metallic characteristics with significant contributions from Li and interstitial quasiatoms near the Fermi level. Electron-phonon coupling simulations predict superconducting transition temperatures of 5.8 K for ${\mathrm{Li}}₄\mathrm{Bi}$ and 6.5 K for ${\mathrm{Li}}₅\mathrm{Bi}$ at 100 GPa. High-temperature molecular dynamics simulations reveal superionic behavior in ${\mathrm{Li}}₄\mathrm{Bi}$ at 2400 K and 100 GPa, driven by cross-layer lithium diffusion, with further heating leading to a liquid phase transition. In contrast, ${\mathrm{Li}}₃\mathrm{Bi}$ is a pressure-tunable semiconductor, with an indirect band gap increasing from 0.73 eV at 50 GPa to 0.98 eV at 150 GPa. This study reveals the diverse physical properties of lithium-bismuth compounds under high pressures and provides a foundation for exploring their potential applications.