Structural, Mechanical, and Electronic Properties of High-Hardness Silicon Tetranitride

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: Si₆N with <i>P</i>-1 symmetry and SiN₄ with space group <i>R</i>-3<i>c</i>. Phonon spectra and ab initio molecular dynamics simulations confirm the dynamical and thermal stability of <i>R</i>-3<i>c</i> SiN₄ at ambient pressure and up to 2000 K. Notably, <i>R</i>-3<i>c</i> SiN₄ 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, SiN₄ 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 SiN₄ 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.