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In this paper, Ni70Mn25Co5 and Fe64Ni36 alloys and their composite alloys were used as catalysts to study the growth characteristics of typeⅠb diamonds grown along (100) crystal plane at different temperatures under 5.6 GPa pressure by high temperature and high pressure temperature gradient method. The results show that the diamond synthesized with Fe64Ni36 catalyst has a cracking growth zone of about 50 K in the high temperature growth range of (111) crystal plane. The diamond synthesized with Ni70Mn25Co5 catalyst is prone to crystal stock defects in the growth range, especially in the high temperature crystal growth range of (111) crystal plane. The excessive melting of Fe64Ni36 catalyst at high temperature may be the cause of crystal cracking, and the low viscosity of Ni70Mn25Co5catalyst melt may be the reason for easy formation of crystal stock. The combination of two kinds of catalysts can effectively avoid the formation of cracking and crystal stock. Raman spectroscopic characterization shows that the internal quality of crystal stock is similar to that of single crystals. There are more lattice distortion and impurities in the cracky crystals and the stress in the crystal is larger. The diamond crystal synthesized by compound catalyst system has low internal stress and good quality. [ABSTRACT FROM AUTHOR]

Doping is an important means to control the properties of diamond. In this paper, the P-doped diamond large single crystals were synthesized by temperature gradient method at 5. 6 GPa and 1 312 ℃ using Fe3P as the phosphorus source. The results of the optical micrographs of diamond samples show that as the amount of Fe3P additve increases, the color of diamond crystals becomes darker, the number of inclusions increases in the crystals, and the crystal shape transforms from plate to tower, even to skeletal. It indicates that the V-shaped growth region shifts to the right when Fe3P is added. This is due to Fe3P has effect on the properties of the catalyst. IR spectra of P-doped diamond reveal that the concentrations of nitrogen impurity in the diamond crystals increases with the increase of the Fe3P content. It indicates that the entry of phosphorus induces nitrogen atoms to enter the diamond lattice more easily. Raman spectra results show that with the increase of Fe3P content, the Raman peak positions of the synthesized diamond change little, but the FWHM becomes larger. This suggests that the entry of phosphorus increases the crystal lattice distortion of diamond. XPS test results show that with the increase of Fe3P, the content of P relative to C in diamond crystal also increases. It means that phosphorus are present in the diamond crystals synthesized by Fe3P addition. [ABSTRACT FROM AUTHOR]

It is of great academic value to study the influence of carbonate doping on the growth behavior of synthetic diamond crystals. In this paper, CaCO3 was doped into the carbon source in the diamond synthesis cavity at different ratios using the temperature gradient method at high pressure and high temperature (HPHT). The purpose of the study is to investigate the effect of CaCO3 doping on the growth behavior of diamond along the (100) or (111) crystal plane, respectively. The crystal morphology of doped synthetic diamonds was studied by optical microscopy. The results show that with the increase of the CaCO3 content, the crystal shape of diamond growing along the (100) plane change from tower to plate accompanied by crack crystal or crystals stock. The color of the crystal becomes lighter and then darker, and the inclusions appear in diamond. Besides, the crystal shape of diamond growing along (111) surface gradually changes from plate to tower accompanied by crack and twin crystals phenomena. With the increase of the CaCO3 content, the color of diamond crystals gradually becomes darker, and more inclusions appear in diamond. The Raman spectroscopy results show that with the increase of CaCO3 content, the Raman peak position shifts of doped diamond growing along (100) or (111) plane increase, and the full width at half maximum (FWHM) becomes larger. This indicates that the doping of CaCO3 increases crystal lattice distortion and internal stress of diamond. In this paper, the causes for the effect of CaCO3 doping on the crystal shape, color, internal quality and other behaviors of the diamond growing along the two different faces were analyzed, which lays the foundation for the subsequent study of this topic. [ABSTRACT FROM AUTHOR]