High-pressure phases and pressure-induced phase transition of MoN6 and ReN6

Highlights: • Two new transition metal nitride structures (MoN₆ and ReN₆) are proposed. • The phase transition of MoN₆ is revealed. • Energetic N₆ in MoN₆ and ReN₆ structures indicate that they may be potential high energy density materials. -- Abstract: Transition metal nitrides have been widely used in many scientific and technical areas because of their unique physical and mechanical properties. We report two new nitrogen-rich transition metal nitrides, MoN₆ and ReN₆, by crystal structure searching technique. Under high pressure, MoN₆ will undergo phase transition (from R-3m to Pm-3 phase) at 54 GPa, and ReN₆ always keep the R-3m phase in the pressure range from 50 to 100 GPa. There are benzene-like six-membered "N6" rings with nitrogen single bonds in the R-3m phase structures, indicating that MoN₆ and ReN₆ are expected to be the high-energy-density materials.