High-pressure synthesis and characterization of diamond from an Mg–Si–C system

Abstract

Diamond crystallization in the Mg–Si–C system has been studied at high-pressure high-temperature conditions of 7 GPa and 1500–1900 °C. The features of nucleation and growth of diamond from the carbon solution in the Mg–Si melt are established. The degree of the graphite-to-diamond transformation is found to depend significantly on the crystallization temperature. As opposed to the pure Mg–C system where the cubic morphology dominates, the octahedron with the antiskeletal structure of faces is the dominant form of growth in the Mg–Si–C system over the entire temperature range. The possibility of epitaxial growth of silicon carbide tetrahedral crystals on diamond upon their co-crystallization was noted. Synthesized diamonds are found to contain optically active silicon-vacancy (Si-V) centers and inactive substitutional silicon defects, giving rise to the 1.68 eV system in the photoluminescence spectra and an absorption peak at 1338 cm⁻¹ in the infrared absorption spectra, respectively.