Predicting the Crystal Structures and Properties of Lithium-Carbon-Nitrogen Phases under Pressure

Nitrogen-containing high-energy-density materials (HEDM) have attracted significant attention due to their wide range of applications. However, achieving a balance between stabilization and detonation performance remains a challenge. In this study, we employ crystal structure prediction combined with first-principles calculations to explore the stable and metastable (kinetically stable) structures of Li-C-N ternary compounds under pressures ranging from 0 to 100 GPa. We identify a series of ternary phases, including C2/m LiC₂N₂, P1̅ Li₃CN₂, Pca2₁ Li₂CN₂, and P2 Li₈CN₄, which are stable at 50 GPa. Additionally, six metastable phases were selected based on our stability criteria. Among these, P2/m LiC₂N₄, P2/m LiCN₃, and P/m Li₃C₄N₁₀ demonstrate excellent detonation properties and are recoverable at atmospheric pressure and high temperature, making them promising candidates for further experimental investigation. Notably, we report for the first time that the pyrazinacene-based C2/m LiC₂N₂ phase exhibits superconducting properties at 50 GPa with a calculated T_c of 2.3 K and reaches a maximum of 24.6 K at 250 GPa. Furthermore, the thermodynamically metastable C2/m C₂N₂ and Pnnm Li₂C₂N₂ phases are dynamically stable at 50 GPa, and they complete this pyrazinacene-based n-type materials family.