Effect of Nitrogen Pressure on the Structure of Cr-N, Ta-N, Mo-N, and W-N Nanocrystals Synthesized by Arc Discharge

The effect of nitrogen pressure on the structure of Ta-N, Cr-N, Mo-N, and W-N nanocrystals formed in arc discharge process was investigated. At the nitrogen pressure of 5 similar to 20 kPa, the pure cubic-phase TaN and CrN nanocrystals were formed, whereas pure cubic phase of Mo2N and W2N cannot be obtained. A little of metal Mo and a mass of metal W were mixed with the products of Mo2N and W2N, respectively. At the nitrogen pressure of 30 similar to 50 kPa, subnitride Ta2N and Cr2N and metal Cr were gradually formed in the product; furthermore, the proportion of metal Mo and W increased in the product of Mo2N and W2N, respectively. It indicated that the low nitrogen pressure makes cubic mononitride formation favorable. We explain this experimental observation in terms of the evaporation rate of anode metal and the ionization of nitrogen.