Diamond Crystallization from a Sulfur―Carbon System at HPHT Conditions

In this paper, we report on diamond synthesis in the sulfur−carbon (S−C) system at temperatures in the range of 1550−2000 °C and pressures of 6.3−7.5 GPa. It is established that crystallization of carbon phases (diamond and graphite), the degree of the graphite-to-diamond conversion, and diamond crystal morphology are primarily determined by the pressure−temperature (P−T) conditions. It is suggested that the most probable medium of diamond crystallization in the S−C system is the melting of carbon disulfide CS2. Fourier transform infrared (FTIR) microspectroscopy revealed that synthesized diamond crystals contained nitrogen impurity in the form of A and C defects with a total nitrogen concentration up to 1500 ppm. For the crystals with high nitrogen content, hydrogen-related centers are typically observed. Addition of water to the S−C system results in a decrease in the diamond synthesis temperature and a change in diamond crystal morphology from cuboctahedron to octahedron.