Polymerization of nitrogen in two theoretically predicted high-energy compounds ScN6 and ScN7 under modest pressure

Abstract Materials under high pressure usually exhibit unique chemical and physical properties. Polynitrogen compounds have received widespread attention as potential high energy density materials. This paper uses CALYPSO crystal structure prediction method to study the structures of ScN 6 and ScN 7 in 0–100 GPa. Theoretical calculations show that ScN 6 is thermodynamically stable above 80 GPa, while ScN 7 is thermodynamically stable from 30 GPa to 90 GPa. Furthermore, ScN 7 is metastable under ambient conditions, demonstrating that it can be quenched to ambient conditions after high pressure synthesis. The P 1 ¯ -ScN 6 is a three-dimensional extended fold multi-nitrogen network, and the P 1 ¯ -ScN 7 contains a five-membered ring and a curved N4 molecular unit. Both P 1 ¯ -ScN 6 and P 1 ¯ -ScN 7 contain a lot of N–N single bonds and N=N double bonds. The energy densities of P 1 ¯ -ScN 6 and P 1 ¯ -ScN 7 are 3.97 kJ g −1 and 3.12 kJ g −1 , respectively. The detonation velocity and detonation pressure of the P 1 ¯ -ScN 6 phase and P 1 ¯ -ScN 7 phase are also higher than that of TNT. Excellent energy storage properties and detonation performance show that they can be used as potential high-energy materials. These results opened up a new way for the synthesis of nitrogen-rich compounds.