Bingmin Yan

Synthesis and characterization of hydrogen-doped diamond under high pressure and high temperature

To investigate the effect of the hydrogen element on diamond crystallization, hydrogen doped diamond crystals are synthesized at 5.0–6.0 GPa and 1250–1600 °C by adding ferrocene (C10H10Fe) to a system of carbon and Fe-based solvent–catalyst. The essential dependence of diamond morphology and nucleation on the composition of the crystallization medium is established in the P–T diagram. It is found that the growth region of the {111} face becomes wider, while the region of the {100} face becomes narrower and almost disappears with increasing concentration of C10H10Fe. The changing of the diamond growth habits can be explained by the effect of hydrogen from the decomposition of C10H10Fe on diamond crystallization. Fourier transform infrared absorption spectra reveal that the hydrogen-related peaks increase with an enhancement in the ratio of C10H10Fe additive. The observed Raman shift is due to the doping of hydrogen atoms into the diamond lattice. In addition, we find that the change of characteristics of the growth medium of the diamond crystal induced by hydrogen is an important factor for the changes of the synthesis conditions, the growth rate and the nitrogen concentration of the synthesized diamond.

Influence of carbon convection field on high quality large single crystal diamonds morphology under high pressure and high temperature

The temperature and convection fields of a catalyst with three different heights were simulated in a temperature gradient growth (TGG) system under high pressure and high temperature (HPHT) conditions. Temperature fields were simulated to rule out the influence of temperature on the crystal morphology. The features of the calculated convection field could predict the particular situations of diamond growth systems very well, and could explain the change of diamond morphology accompanying the growth process. According to the calculated results, we predict that the morphology of a diamond crystal changes from cubic crystal to cub-octahedral. A good agreement has been obtained between the calculated results and the observed experimental data. The morphology and structural properties of the synthesized samples are characterized by optical microscopy and a Raman spectrum. The results illustrate that the synthesized diamond crystals have less lattice distortion and with high quality.

Studying the effect of hydrogen on diamond growth by adding C10H10Fe under high pressures and high temperatures

ABSTRACT In this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C10H10Fe additive, high pressures and high temperatures range of 5.2–6.2 GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C10H10Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated with hydrogen atoms.

Effects of catalyst height on diamond crystal morphology under high pressure and high temperature

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth (TGG) under high pressure and high temperature (HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub-octahedral shape as the catalyst height rises. Moreover, the finite element method (FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.