The effect of pressure on synthetic diamond crystals at high temperatures and pressures in an Fe/Ni catalyst system

Abstract

Pressure is a necessary condition for the growth of natural diamond. Studying the effect of pressure on the nitrogen content of diamond is important for exploring the growth mechanism of natural diamond and the formation of different types of natural diamond. We studied the characteristics of synthetic diamond crystals under various pressures using large-volume cubic high-pressure apparatus with an Fe/Ni alloy as a catalyst under the pressures of 5.5 to 6.5 GPa and temperatures of 1300 °C to 1400 °C. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that increasing the pressure in a nitrogen-doped system decreased the nitrogen content inside the diamond. The increase in pressure led to an increase in the proportion of A-center nitrogen in nitrogen-doped diamond, which plays an important role in exploring the formation of natural Ia diamonds. Raman spectroscopy and X-ray diffraction analysis showed that a type Ib diamond single crystal has a high-quality sp³ structure. Increasing the pressure in the nitrogen doped system can improve the quality of synthetic diamond, which can be proved by the decrease of Raman FWHM.