Crystal structure of and displacive phase transition in tungsten nitride WN

The crystal structure and stability of tungsten mononitride WN have been elusive. In this study, a new type of WN has been identified, which has a MnP-type structure. We show that the NiAs-type WN proposed before is the high-pressure high-symmetry form of the MnP-type WN. There is a displacive phase transition between the two structures at about 89 GPa. The stabilization of metal nitrides at high pressures in the same structure types of the corresponding phosphides has been rationalized based on the formation conditions of chemical bonds. For the structures that are stable in metal phosphides or silicides but not in nitrides or carbides at the ambient pressure, it is highly possible to stabilize them in nitrides or carbides at high pressures.