High-Pressure Synthesis and Crystal Structure of MoC-Type Tungsten Nitride by Nitridation with Ammonium Chloride.

A novel tungsten nitride, MoC-type WN, was synthesized at 6 GPa and 1200 °C via nitridation of tungsten by ammonium chloride as a nitrogen source. This compound is isostructural with γ'-MoC, which has a hexagonal structure with a space group of P63/mmc (No. 194). Micrometer-sized single crystals of MoC-type WN were grown in molten ammonium chloride flux. In addition, NaCl-type WN and WC-type WN were synthesized via nitridation by ammonium chloride at 6 GPa and 1000 °C. Ammonium chloride is appropriate as a nitrogen source for nitride synthesis under high pressure. The new WN phase crystallizes in the hexagonal structure with unit cell parameters of a = 2.89248(2) Å and c = 10.17069(7) Å. The chemical formula of MoC-type WN refined by the Rietveld analysis from powder X-ray diffraction data was WN0.60(1). The zero-pressure bulk modulus, K0, of MoC-type WN was determined to be 338(3) GPa, which can be expected to be a hard material.