Predictions on High-Power Trivalent Metal Pentazolate Salts

High-energy-density materials (HEDMs) have been intensively studied for their significance in fundamental sciences and practical applications. Here, using the molecular crystal structure search method based on first-principles calculations, we have predicted a series of metastable energetic trivalent metal pentazolate salts MN15 (M= Al, Ga, Sc, and Y). These compounds have high energy densities, with the highest nitrogen content among the studied nitrides so far. Pentazolate N-5(-) molecules stack up face-to-face and form wave-like patterns in the C222(1) and Cc symmetries. The strong covalent bonding and very weak noncovalent interactions with nonbonded overlaps coexist in these ionic-like structures. We find MN15 molecular structures are mechanically stable up to high temperature (similar to 1000 K) and ambient pressure. More importantly, these trivalent metal pentazolate salts have high detonation pressure (similar to 80 GPa) and velocity (similar to 12 km/s). Their detonation pressures exceeding that of TNT and HMX make them good candidates for high-brisance green energetic materials.