In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high ...In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT).The HPHT synthesis conditions were about 5.5 GPa and 1500-1550 K.Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy.The effects of additive NaN3 on crystal growth habit were investigated in detail.The crystal morphology,nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra,respectively.The results show that with an increase of the content of NaN3 added in the synthesis system,the region of synthesis temperature for high-quality diamond becomes narrow,and crystal growth rate is restricted,whereas the nitrogen concentration in synthetic diamond increases.Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers).The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.展开更多
In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. O...In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst. The crystal color changes from yellow to nearly colorless. The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive. The lowest synthesis conditions fell first and then rose with increasing aluminum. We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.展开更多
文摘In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT).The HPHT synthesis conditions were about 5.5 GPa and 1500-1550 K.Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy.The effects of additive NaN3 on crystal growth habit were investigated in detail.The crystal morphology,nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra,respectively.The results show that with an increase of the content of NaN3 added in the synthesis system,the region of synthesis temperature for high-quality diamond becomes narrow,and crystal growth rate is restricted,whereas the nitrogen concentration in synthetic diamond increases.Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers).The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.
基金supported by the New Century Excellent Talents in University and the National Natural Science Foundation of China (Grant Nos.50572032,50731006 and 50801030)
文摘In this paper, we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500℃. Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst. The crystal color changes from yellow to nearly colorless. The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive. The lowest synthesis conditions fell first and then rose with increasing aluminum. We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.
