Comprehensive Investigation of Structural and Mechanical Characteristics of Crystalline C3n4 Under High Pressure

This study provides a comprehensive examination of crystalline C3N4, investigating seven distinct phases across a pressure range of 0-150 GPa using the GGA-PBE method. Key findings include phase transitions from g-C3N4 at 0 GPa to α-C3N4 (P31c) at 9.08 GPa, ultimately forming cubic C3N4 (I-43d) at 95.26 GPa. Additionally, at 0 GPa, the minimal enthalpy difference between P-6m2 and R3m structures suggests possible coexistence, implying multiple structural coexistences. The enthalpy difference between α-C3N4 and β-C3N4 structures also hints at potential coexistence. The study delves into pressure-dependent mechanical properties, including variations in elastic constants and major moduli with pressure. However, concerns arise about the potential instability of g-C3N4 under high pressure, as indicated by stability conditions.