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The crystal stock defect was formed in growing for a long time (22 h) of plate type Ib large diamond single crystals from the NiMnCo−C system at high pressure and high temperature (HPHT). The existence of crystal stock defect has great influence on the synthesis of high quality and large size diamond single crystal. In this paper, the effects of crystal growth rate and catalyst components on diamond crystal stock defects are studied. Firstly, the results show that the growth rate of diamond crystals is closely related to the generating of diamond crystal stock. This defect can be eliminated as the growth rate of diamond crystal synthesized with NiMnCo catalyst is reduced to less than 3 mg/h. Secondly, the composition of the catalyst also affects the formation of the crystal stock. High viscous FeNi catalyst is used to grow high quality large single crystals of diamonds at a growth rate of 3.18 mg/h for a long time (22 h). Thirdly, the effect of catalyst composition on diamond crystal stock was analyzed by testing the micro-morphology and nitrogen content of diamond. It can be shown from the results by scanning electron microscopy (SEM) that the surface of crystals synthesized with low-viscosity catalyst is rough, while it synthesized with high-viscosity catalyst is smooth. It was found from the test results of micro Fourier-transform infrared spectroscopy (FTIR) that the content of nitrogen in the crystals synthesized with FeNi catalyst was much lower than that in the crystals synthesized with NiMnCo. FeNi catalyst can effectively avoid the crystal stock, and is more suitable for the growth of large-size and high-quality diamond single crystal. Changing the composition of the catalyst is an effective way to avoid the crystal stock phenomenon.

Large single crystal diamonds were synthesized using Ti/TiC and Cu as additives in the Fe64Ni36-C system under 5.6 GPa and at 1543 K. The synthesized crystals were characterized by optical microscopy and infrared spectroscopy. Results show that both Ti and TiC react with N to form TiN and Ti (C1-x, Nx), respectively, which leads to a poor nitrogen removal efficiency and a large number of inclusions and pits in the crystals. Co-doping TiorTiC with Cu promotes the decomposition of TiC to release Ti, which improves the nitrogen removal efficiency, and thereby reduces the number of defects and inclusions in the diamond crystals. A high-quality type IIa diamond crystal was optimally synthesized when the Ti/Cu contents were 1.70 wt.%/1.06 wt.% (Ti: Cu = 4: 2.5).

Ti3SiC2, a ternary carbide, was proposed at this paper to use as the binder of polycrystalline diamonds to overcome the weaknesses of traditional metal binders and ceramic binders. Ti3SiC2was first reported to be in-situ synthesized under high pressure (4GPa) and at high temperature (1400°C) (HPHT) from the mixtures of Ti, Si and graphite powders or the mixture of Ti, SiC and graphite powders. Ti3SiC2-damond composites were also made at HPHT from the previous mixtures and diamond particles. TiCx, Ti5Si3Cxand TiSi2were main impurities and/or intermediate products of Ti3SiC2samples synthesized at HPHT. Ti3SiC2content increased as synthesized time increased from 10 min to 60 min. For as-synthesized composites, diamond particles were evenly distributed in matrix. The diamond particles are bonded well with the matrix by three types of interface.

With adopting Al as the nitrogen getter in Ni70Mn25Co5 or Fe55Ni29Co16 catalyst, High-quality type-Ⅱa large diamonds have been grown under the conditions of about 5.5GPa and 1580K by using the temperature gradient method. While Al(2.0wt%) is added in the Fe55Ni29Co16, the nitrogen concentration(Nc) in the diamond is less than 1ppm. While Al(4.0wt%) is added in the Ni70Mn25Co5, the Nc in the diamond is highly arrived at 48ppm. The different of solubility of nitrogen in both catalyst at high pressure and high temperature is the basic reason of the different effect of eliminating nitrogen of Al. It can be shown in experamentals that Al is a less efficient nitrogen getter in Ni70Mn25Co5 than in Fe55Ni29Co16. While Al(2.0wt%) is added in the Fe55Ni29Co16, the high-quality type-Ⅱa large diamond, in which nitrogen is less than 1ppm and which the size was arrived at 3.3mm, had grown by decreasing the growth rate of diamond.

As is well known, diamond is extensively used in many fields, because of its excellent properties, such as its hardness, high thermal conductivity, high electron and hole mobility, high breakdown field strength and large band gap (5.4 eV). However, its application in semiconductor area needs to be further understood, because it is irreplaceable by conventional semiconductor materials, especially in the extreme working conditions. Furthermore, the preparation of n-type diamond semiconductors is still an unsolved problem. The reason is that an effective donor element has not yet been found. Recently, both the theoretical and experimental studies show that it is difficult to obtain n-type diamond semiconductor with excellent properties by doping single element in the synthetic system. In this paper, diamond single crystals co-doped with B and S are successfully synthesized in FeNiMnCo-C system at a pressure of 6.5 GPa and temperature ranging from 1280 ℃ to 1300 ℃, by using temperature gradient method. The impurity defects in the synthesized diamond single crystals are characterized by Fourier infrared absorption spectra and the results indicate that the corresponding characteristic absorption peaks of B and S are located at 1298 cm–1 and 847 cm–1, respectively. Furthermore, the absorption attributed to B-S group is not detected. The N concentration of the synthesized diamond crystals decreases to 195 ppm, resulting from the incorporation of B and S impurities into the diamond lattices. Additionally, the electrical properties of the typical diamond single crystals are measured in virtue of Hall effects at room temperature. The measurement results display that the electrical conductivity of the diamond doped with B is obviously enhanced, resulting from the involvement of the S when B addition amount is fixed in the synthesis system. Hall mobility of the corresponding diamond crystals increases from 12.5 cm–2·V–1·s–1 to 760.87 cm–2·V–1·s–1. And then, the relative proportion of S and B will determine the p/n properties of the obtained diamond. In order to further study the electrical properties of diamond, first-principles calculations are adopted and the theoretical calculation results show that the impurity elements involved in the obtained diamond can affect the band structures of the synthetic diamond crystals, which is consistent with the experimental result.

In this paper, diamond single crystal co-doped with sulfur and boron was successfully synthesized at the fixed pressure of 6.0 GPa and temperature range of 1535 K. Sulfur was detected in the co-doped diamond by Fourier Transform Infrared Spectroscopy (FTIR) and the corresponding characteristic peak located at 848 cm-1. Interestingly, Hall effect measurements indicated that the diamond co-doped with sulfur and boron exhibited n-type semiconductor behaviour. Furthermore, the Hall mobility and carrier concentration of the co-doped diamond higher than those of the boron-doping diamond.

This paper proposes a new passivity-based control method for APF. Such method introduces damping matrix R a to improve harmonic compensation effect and accelerate the convergence speed. It also includes Robust stability analysis and the results proved that APF system can still maintain stable after the parameter variation and load disturbance. Based on the Robust analysis, the control equations are further simplified to make them more realizable. This new passive current control strategy is supported by simulation results.