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High-quality type IIa large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi–C system at temperature ranging from 1230 °C to 1380 °C and at pressure 5.3–5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the FeNi–C system to investigate the best ratio for high-quality type IIa diamond. Then, the different content of nitrogen getter Ti/Cu (Ti : Cu = 4 : 3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared (FTIR), are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter. Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25 °C higher than that of type Ib diamond. With the increase of the content of Ti/Cu (Ti : Cu = 4 : 3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm. The SEM results show that the synthesized crystals are mainly composed by (111) and (100) surfaces, including (311) surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type IIa diamond. [ABSTRACT FROM AUTHOR]

This paper reports the crystal growth of diamond from the FeNi–Carbon system with additive phosphorus at high pressures and high temperatures of 5.4–5.8 GPa and 1280–1360 °C. Attributed to the presence of additive phosphorus, the pressure and temperature condition, morphology, and color of diamond crystals change obviously. The pressure and temperature condition of diamond growth increases evidently with the increase of additive phosphorus content and results in the moving up of the V-shape region. The surfaces of the diamonds also become coarse as the additive phosphorus added in the growth system. Raman spectra indicate that diamonds grown from the FeNi-phosphorus-carbon system have more crystal defects and impurities. This work provides a new way to enrich the doping of diamond and improve the experimental exploration for future material applications. [ABSTRACT FROM AUTHOR]