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 <i>C</i>2/<i>m</i> LiC₂N₂, <i>P</i>1̅ Li₃CN₂, <i>Pca</i>2₁ Li₂CN₂, and <i>P</i>2 Li₈CN₄, which are stable at 50 GPa. Additionally, six metastable phases were selected based on our stability criteria. Among these, <i>P</i>2/<i>m</i> LiC₂N₄, <i>P</i>2/<i>m</i> LiCN₃, and <i>P</i>/<i>m</i> 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 <i>C</i>2/<i>m</i> LiC₂N₂ phase exhibits superconducting properties at 50 GPa with a calculated <i>T</i>_c of 2.3 K and reaches a maximum of 24.6 K at 250 GPa. Furthermore, the thermodynamically metastable <i>C</i>2/<i>m</i> C₂N₂ and <i>Pnnm</i> Li₂C₂N₂ phases are dynamically stable at 50 GPa, and they complete this pyrazinacene-based n-type materials family.