Effect of catalyst composition on growth and crack defects of large diamond single crystal under high temperature and pressure br

Under the condition of 5.6 GPa and 1250-1450 degrees C, the diamond single crystals are synthesized in a cubicanvil high-pressure and high-temperature apparatus. High-purity FeNiCo solvents or NiMnCo solvents arechosen as the catalysts. High-purity (99.99%) graphite powders selected as a carbon source. High-qualityabrasive grade diamond single crystals with relatively developed (100) or (111) crystal planes are used as crystalseeds. The effects of catalyst composition on crack defects in diamond single crystals are studied carefully.Firstly, using FeNiCo and NiMnCo catalysts respectively, we carry out the diamond single crystal growthexperiments. It is found that under the same crystal growth condition, the probability of crystal crack defects indiamond single crystals grown with FeNiCo catalyst is significantly higher than that of crystals grown withNiMnCo 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 thestability of growth conditions. Secondly, the relationship between the growth time and the limit weight gainspeed of the diamond single crystal synthesized, respectively, by FeNiCo catalyst and NiMnCo catalyst areinvestigated. The results are shown below. 1) The limiting growth rate of diamond single crystal increases withthe growth time going by. 2) In the same growth time, the limit growth rate of diamond crystal grown withNiMnCo catalyst is higher than that of diamond crystal grown with NiMnCo catalyst. Thirdly, by scanningelectron microscopy (SEM), we calibrate the surface morphology of the synthesized diamond single crystal. Thetest results show that the diamond single crystal has a high surface flatness. Even for the crystals with crackdefects in the interior, the surface flatness is still good. However, Fourier transform infrared (FTIR)measurements show that the nitrogen impurity content of diamond crystal grown by FeNiCo catalyst withcrack defect is about 3.66x10-4. The content of nitrogen impurity in the crystal grown by NiMnCo catalystwithout crack defect is about 4.88x10-4. The results show that there is no direct correlation between nitrogenimpurity content and crack defects in diamond crystal