Effect of catalyst composition on growth and crack defects of diamond single crystals by HPHT

In the paper, under 5.6 GPa and 1250-1450℃, the diamond single crystals were synthesized in a cubic anvil high pressure and high temperature apparatus. High-purity FeNiCo solvents or NiMnCo solvents were chosen as the catalysts. High-purity graphite powder (99.99%, purity) was selected as the carbon source. High quality abrasive grade diamond single crystals with relatively developed (100) or (111) crystal planes were used as crystal seeds The effects of catalyst composition on crack defects in diamond single crystals were studied carefully. At first, using FeNiCo and NiMnCo catalysts respectively, we carried out diamond single crystal growth experiments. It is found that under the same crystal growth conditions, the probability of crystal crack defects in diamond single crystals grown with FeNiCo catalyst is significantly higher than that of crystals grown with NiMnCo catalyst. We believe that this is related to the high viscosity, poor fluidity of FeNiCo catalyst melt and the large specific surface area of the crystal during growth, which leads to its high requirements for the stability of growth conditions. Secondly, the relationship between the growth times and the limit weight gain speed of the diamond single crystals synthesized by choosing FeNiCo catalyst and NiMnCo catalyst were investigated. The results show that: (i) The limiting growth rate of diamond single crystals increases with the growth time. (ii) At the same growth time, the limit growth rate of diamond crystal grown with NiMnCo catalyst is higher than that of diamond crystal grown with NiMnCo catalyst. Thirdly, by means of scanning electron microscopy (SEM), we calibrated the surface morphology of the synthesized diamond single crystals. The test results show that the diamond single crystal has a high surface flatness. Even for crystals with crack defects in the interior, the surface flatness is still good.. However, by Fourier transform infrared (FTIR) measurements, the researchers obtained that the nitrogen impurity content of diamond crystal grown by FeNiCo catalyst with crack defect is about 366 ppm. The content of nitrogen impurity in the crystal grown by NiMnCo catalyst without crack defect is about 488 ppm. The results show that there is no direct correlation between nitrogen impurity content and crack defects in diamond crystals.