High-pressure formation of antimony nitrides: a first-principles study

The structural phase transition, electronic properties, and bonding properties of antimony nitrides have been studied by using the first principles projector augmented wave method. The relationship between the formation enthalpy and the composition of the Sb-N system has been explored. The novel Sb₂N₃ with the Cmcm space group is stable in a narrow pressure range from 100 GPa to 120 GPa. Apart from the Sb₂N₃, two nitrogen-rich phases SbN₂ and SbN₄ were predicted. The SbN₂ with the C2/m space group is stable at 12 GPa and then transforms to the high-pressure phase at 23 GPa. The nitrogen-rich SbN₄ appears at 14 GPa then undergoes C2/m → P1̄ → P1̄ phase transitions, and the calculated pressures of the phase transitions are 31 and 60 GPa, respectively. The nitrogen-rich SbN₂ and SbN₄ have similar structural features. Both SbN₂ and SbN₄ can be seen as a sandwich structure composed of the Sb-N layers and N₂ dimers. The pressure-induced phase transitions of SbN₂ and SbN₄ are accompanied by the electron transfer between the Sb-N layers and N₂ dimers. Moreover, the nitrogen-rich SbN₄ has a higher energy density of 2.42 kJ g^-1 and is a potentially high energy density material.