The recent experimental syntheses of carbon nitrides ($\mathit{oP}\text{8-CN}, tI14\text{−}{\mathrm{C}}_3{\mathrm{N}}_4, tI24\text{-C}{\mathrm{N}}_2$, and $hP126\text{−}{\mathrm{C}}_3{\mathrm{N}}_4$) have created great scientific interest in the long-standing debate on their stability, ultra-incompressibility, and superhardness [D. Laniel et al., Adv. Mater. 36, 2308030 (2024)]. Herein, this study presents a systematic investigation of pressure-induced variations in thermodynamic and dynamic stability for these materials using high-throughput first-principles calculations. The results demonstrate that all structures transition from thermodynamic instability at ambient pressure to stability under high pressure, showing excellent agreement with experimental results. Mechanical characterization at ambient conditions reveals intrinsic ultra-incompressibility and superhard characteristics across the series, with exceptional bulk moduli (339–399 GPa) and ideal strength values (37.8–41.8 GPa). Within the maximum pressure range considered, up to 160 GPa, bulk moduli increase by 238–260% and ideal strength improves by 181–327% compared to ambient-pressure values. Analysis of bond deformation trajectories reveals that the mechanical anisotropy originates from the cooperative alignment of C-N tetrahedral units. Electronic structure analysis shows that pressure-induced charge accumulation enhances $sp$-orbital hybridization between C and N atoms while suppressing electronic reorganization of N lone pairs, governing structural strengthening and toughening mechanisms. These findings advance the understanding of the newly synthesized C-N superhard materials, and they provide theoretical guidance for strengthening mechanisms under extreme high pressures.

Close

PrevNext

View figure in article

• Charge
• Charge density waves
• Density of states
• Elasticity
• Fermi surface
• Fracture
• Hardness
• Mechanical deformation
• Plasticity
• Stress