Effect of Nitrogen Impurity on Diamond Crystal Growth Processes

In this paper, we report on the influence of nitrogen concentration in metal melts on the growth processes, morphology, and defect-and-impurity structure of diamond crystals. In two series of experiments, the concentration of nitrogen in the growth system was varied by adding Fe 3 N and CaCN 2 to the charge; the other parameters and conditions of the growth were constant: FeNiC system, P = 5.5 GPa, T = 1400 °C, and duration of 65 h. It has been found that, with increasing nitrogen concentration ( C N ) in the metal melt from 0.005 to 0.6 atom %, the growth of single crystal diamond is followed by formation of aggregates of block twinned crystals and then by crystallization of metastable graphite. At the stage of single crystal growth, an increase in C N results in an increase in nitrogen impurity concentration in diamond crystals from about 200 ppm to approximately 1100 ppm, an increase in density of dislocations, twin lamellae, and internal strains, and a change in crystal morphology. Further increases in C N result in formation of aggregates of block crystals with nitrogen concentration around 120−300 ppm. At nitrogen concentration in the melt higher than a certain critical value, nucleation and growth of diamond are terminated and graphite crystallizes in the diamond stability field.