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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]

The inclusions in large diamond single crystals have effects on its ultimate performance, which restricts its industrial applications to a great extent. Therefore, it is necessary to study the inclusions systematically. In this paper, large diamond single crystals with different content values of inclusions are synthesized along the (100) surface by the temperature gradient method (TGM) under 5.6 GPa at different temperatures. With the synthetic temperature changing from 1200 °C to 1270 °C, the shapes of diamonds change from plate to low tower, to high tower, even to steeple. From the microscopic photographs of the diamond samples, it can be observed that with the shapes of the samples changing at different temperatures, the content values of inclusions in diamonds become zero, a little, much and most, correspondingly. Consequently, with the temperature growing from low to high, the content values of inclusions in crystals increase. The origin of inclusions is explained by the difference in growth rate between diamond crystal and its surface. The content values of inclusions in diamond samples are quantitatively calculated by testing the densities of diamond samples. And the composition and inclusion content are analyzed by energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). From contrasting scanning electron microscopy (SEM) photographs, it can be found that the more the inclusions in diamond, the more imperfect the diamond surface is. [ABSTRACT FROM AUTHOR]