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 Tc 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.