Coexistence of superconducting and superionic states in lithium boron compounds under high pressure

Lithium-based compounds with interstitial anionic electrons (IAEs) exhibit unique electronic properties, including superconductivity and superionic behavior. The intrinsic connection between these properties offers valuable insights and potential applications in materials science. In this study, we employed machine-learning-accelerated crystal structure prediction and first-principles calculations to investigate the phase stability of various Li–B systems under high pressures. Our results indicate that the known R-3m Li₆B compound is an electride. At 150 GPa, R-3m Li₆B exhibits a superconducting transition temperature of around 51 K and enters a superionic state at high temperatures. Additionally, a monoclinic compound, C2/m LiB₆, which is metastable at ambient pressure, was found. More interestingly, an unpredicted cage-like metallic boron allotrope termed C2/m-B₁₂ can be obtained by removing Li from LiB₆. These findings open avenues for interdisciplinary research and highlight the potential of exotic boron allotropes in advanced device applications.