Stoichiometric and Structural Diversity in the Silicon/Nitrogen Phase Diagram at Atmospheric and High Pressures

In this study, we explore the binary Si–N phase diagram using an ab initio evolutionary algorithm and first-principles calculations at pressures from 0 to 200 GPa. Multiple (meta)stable SixNy phases are predicted, including Si3N2, SiN, Si3N4, SiN2, SiN4, SiN6, and SiN20, with pressure-dependent phase transitions consistent with experimental data for Si3N4 and SiN2. Diverse N-containing species, such as atomic/molecular anions and covalent networks, are identified, with SiN20 arising from cyclo-N5– units and Si(IV) cations. Thermodynamic, dynamic, and thermal stability assessments confirm the viability of these structures, supported by electron- and orbital-based models. Three nitrogen-rich phases SiN4, SiN6, and Si(cyclo-N5)4 are thermally stable up to 400 K at 1 atm, exhibiting detonation properties surpassing TNT, highlighting their potential as high-energy-density materials (HEDM).