Synthesis of hexagonal phases of WN and W2.25N3 by high‐pressure metathesis reaction

Hexagonal tungsten nitrides were synthesized by the metathesis reaction between WCl6 and NaN3 under high pressure and temperature. As well as tungsten mononitride (WN), which is isostructural with hexagonal tungsten carbide (WC), a nitrogen-rich hexagonal compound was also confirmed in the product. The ratio of nitrogen to tungsten was determined to be 1.34 by the quantitative combustion method. The composition was estimated to be W2.25N3 by considering the crystal structure that is best explained by the X-ray diffraction profile. Volume compression measurements under hydrostatic pressure revealed that the WC-type WN has a higher bulk modulus (K-0 = 342 +/- 1 GPa) than that of hexagonal W2.25N3 (K-0 = 291 +/- 2 GPa).