Abstract
Materials with high hardness are critical for industrial and aerospace applications, prompting the search for novel compounds with robust covalent networks. Using a first-principles structure prediction method, we systematically explored the phase stability of Si-N compounds under high pressure. We identified two thermodynamically stable phases: Si(6)N with P-1 symmetry and SiN(4) with space group R-3c. Phonon spectra and ab initio molecular dynamics simulations confirm the dynamical and thermal stability of R-3c SiN(4) at ambient pressure and up to 2000 K. Notably, R-3c SiN(4) exhibits exceptional mechanical properties with a Vickers hardness of 31 GPa, a bulk modulus of 259.53 GPa, and a Young's modulus of 485.38 GPa. Furthermore, SiN(4) possesses a high energy density (1.1 kJ·g(-1)) and outstanding detonation pressure and velocity (228 kbar, 7.11 km·s(-1)), both exceeding those of TNT, making it a potential high-energy-density materials. In addition, electronic structure analysis reveals SiN(4) has a band gap of 2.5 eV, confirming its nonmetallic characteristics and strongly covalent nature. These findings provide theoretical guidance for the future synthesis of Si-N phases and establish a foundation for designing novel materials that combine high hardness with high-energy density performance.