The characteristics of Ib diamond crystals synthesized in a Fe–Ni–C system with different SiC contents

Abstract

Silicon carbide (SiC) is a substance found in natural diamond inclusions. Analyzing the influence of SiC doping on the properties of synthetic diamonds is vital to understanding the growth mechanism of natural diamonds and the material composition of the mantle. In this work, China-type large volume cubic high-pressure apparatus (CHPA) (SPD-6 × 1200) was used to simulate the high-temperature and high-pressure environment of diamond growth. The influence of different SiC doping contents on the crystal characteristics of a Ib-type diamond synthesized in a Fe–Ni–C system was investigated at a pressure of 5.8 GPa and a temperature range of 1650–1670 K. Optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL) were used to characterize the synthesized crystals. The OM results show that the growth rate of the diamond decreases gradually, and the color changes from yellow to light yellow with an increase in the doping concentration. The FTIR results indicate that the nitrogen element in the crystal mainly appears in the diamond crystal in monatomic form (C center). The nitrogen content in the diamond gradually decreases from 275 ppm to 115 ppm with an increase in the SiC dopant ratio. The Raman data show that the FWHM (full width at half maximum) of the diamond crystal increases with an increase in the doping ratio. The XPS results demonstrate that silicon has successfully entered the diamond lattice with a Si–C bond in the crystal. The PL results indicate that the peak intensity of the nitrogen-vacancy (NV⁻) color center (638 nm) in the synthesized diamond crystal increases as the doping ratio increases. As the SiC doping content increases, the peak of the NV⁰ color center (575 nm) appears, and the peak intensity increases.