HTHP synthesis and characterization of 5–8 mm diamond large crystal by Fe-Co alloy catalyst

IIa-type diamonds with 5–8 mm edge lengths were successfully synthesized under the catalytic action of Fe-Co catalyst. The effects of Fe-Co and Fe-Ni catalysts on the synthesis of type Ib diamonds were compared and analyzed. Moreover, the effects of different levels of nitrogen-getter agents on the synthesis of type IIa diamonds were discussed. When we characterized the single diamond crystals, Optical microscopy, Raman spectroscopy, Fourier infrared absorption spectroscopy, and photoluminescence spectroscopy were used. The experimental results showed that the nitrogen content of the diamonds synthesized using Fe-Co alloy catalyst was reduced by 127 ppm compared with those synthesized using Fe-Ni alloy catalyst. When the amount of nitrogen-getter added was increased from 0.4 wt% Ti + 0.5 wt% Cu to 0.7 wt% Ti + 0.8 wt% Cu in the Fe-Co-C system, the nitrogen content in the diamond was reduced from 20 ppm to 1 ppm, the internal crystal stress decreased from 238.1 MPa to 147.4 MPa, and the crystal quality was significantly improved. In addition, the Fe-Co alloy catalysts have a lower V-shaped growth zone of diamond, so its growth region is closer to the graphite-diamond equilibrium line, resulting in slower crystal growth and less impurity content in the crystal. Thus, Fe-Co alloy catalysts can synthesize gem-quality diamonds more easily.