Synthesis of HPHT diamond containing high concentrations of nitrogen impurities using NaN3 as dopant in metal-carbon system

Diamond crystals have been synthesized from FeNi alloy — carbon system under high pressure and temperature of 5.0 to 5.8 GPa and 1500 to 1750 K. Concentrations of the nitrogen impurities of the crystals have been determined from FTIR spectra, and it is found that the concentrations of single substitutional nitrogen impurities exceeds 1000 ppm, when NaN3 is added as dopant to the metal-carbon system. The crystals are 0.2–0.5 mm in diameter with cubo–octahedral morphology, although octahedron and cube were also found in the diamond products. They exhibit yellow green to deep green color.