Additive Ba(N 3) 2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method.Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus.The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated.It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets.The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra.The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form,and the aggregated nitrogen concentration in diamond increases with temperature and duration.In addition,it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature.Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy.Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress,whereas diamond crystals heavily doped with the addition of Ba(N 3) 2 display the tensile stress.
This paper reprots that with Ni-based catalyst/solvent and with a dopant of NaN 3,large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus (SPD-6×1200),and the highest nitrogen concentration reaches approximately 1214-1257 ppm calculated by infrared absorption spectra.The synthesis conditions are about 5.5 GPa and 1240-1300 C.The growth behaviour of diamond with high-nitrogen concentration is investigated in detail.The results show that,with increasing the content of NaN 3 added in synthesis system,the width of synthesis temperature region for growth high-quality diamonds becomes narrower,and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure,the crystal growth rate is slowed down,nevertheless,the nitrogen concentration doped in synthetic diamond increases.
