Synthesis of diamond with high nitrogen concentration from powder catalyst-C-additive NaN3 by HPHT

Diamond crystals with high nitrogen concentration, 1000–2000 ppm, have been successfully synthesized from the system of powder catalyst (Fe–Ni)–C-additive NaN3 in a cubic anvil high-pressure and high-temperature apparatus. The synthetic diamond crystals are cubo-octahedral or octahedral shape with a green or dark green color. The FTIR spectra of the diamond synthesized indicate that its nitrogen concentration increases with an increase of the NaN3 additive. Furthermore, such additive increase also leads to an increase in the minimum temperature and pressure for graphite/diamond conversion. We found iron nitride in the sample synthesized with high content of NaN3. We believe its presence is an indication that Fe content in the Fe–Ni alloy is reduced and the characteristics of catalyst are changed, leading to the increase of the minimum temperature and pressure for graphite/diamond conversion.