Comprehensive computational investigation of structural and mechanical characteristics of crystalline C3N4 under high pressure based on experimental data

Abstract

This study presents a comprehensive investigation of the structural and mechanical characteristics of crystalline C3N4, encompassing seven distinct phases within the pressure range of 0–150 GPa, employing the GGA-PBE method. The analysis reveals significant insights, including the phase transitions of C3N4 from g-C3N4 of P-6m2 at 0 GPa to α-C3N4 of P31c at 9.1 GPa, culminating in c-C3N4 of I-43d at 95.3 GPa. Moreover, the minimal enthalpy difference observed between the gr-C3N4 and g-C3N4 at 0 GPa suggests the potential coexistence of these phases, indicating the likelihood of multiple graphitic carbon nitride structural coexistences at this pressure. The enthalpy difference between α-C3N4 and β-C3N4 structures also indicates the possibility of their coexistence. Furthermore, the study explores the pressure-dependent mechanical properties of C3N4, including changes in elastic constants and major elastic moduli with pressure, though it raises concerns regarding the potential instability of g-C3N4 under high-pressure indicated by calculated stability conditions.