High-pressure synthesis and characterization of diamond from a sulfur-carbon system

Diamond crystallization in the sulfur-graphite system has been studied at P = 7 GPa and T 1750-1850 degreesC in experiments with a duration up to 7 h. It has been found that diamond nucleation and crystallization occur both at the interface between the graphite and sulfur melt and directly within the carbon-saturated sulfur melt. Diamond crystals with maximum size up to 500 mum were synthesized. The crystals had cube-octahedral morphology with minor faces of trapezohedron. Goniometric measurements revealed that crystallographic indexes of the trapezohedron faces are {411} and {944}. Spectroscopic characterization of sulfur-synthesized diamonds by means of infrared absorption microscopy and cathodoluminescence has been made for the first time. It was found that crystals contain nitrogen impurity in the form of A aggregates with concentration up to approximately 700 at. ppm. An absorption band with a maximum at 1050 cm (-1), whose origin is not clear, was observed in the IR spectra. The cathodoluminescence spectra of these diamonds were found to comprise of the well-known H3 and 575-nm systems as well as a broad emission band. (C) 2001 Elsevier Science B.V. All rights reserved.