Exploration of Si-N compounds as high energy density materials

The non-molecular phases of polymeric nitrogen formed under high pressure have potential applications in the area of high energy density materials (HEDMs). Herein, we explored silicon-based nitride materials using a structural search algorithm combined with first-principles calculations. We predicted new phases of SiN₆ that are identified to be metastable together with the previously reported stable compositions of Si₃N₄ and SiN₂. Among these, Cc-SiN₆ consists of a polymeric nitrogen chain, which is quenchable at ambient pressure, suggesting potential applications in HEDMs. Dissociation of SiN₆ can lead to a remarkably high volumetric energy density of 12.81 kJ cm^-3, which is ∼1.3 times larger than that of conventional TNT. Furthermore, an excellent performance in terms of detonation velocity (13.46 km s^-1) and detonation pressure (110.42 GPa) highlights SiN₆ as a promising HEDM. Molecular dynamics simulation using machine-learned potentials for 50 ps indicates that the structure is stable up to 1500 K and can trigger an explosion at nearly 2000 K temperature. The potential of Cc-SiN₆ is evident from its high detonation performance and volumetric energy density, making it ideal for scenarios where compact warhead dimensions are essential. This work highlights the possibility of utilizing silicon-based nitrides to significantly boost the performance of HEDMs.