HPHT synthesis of diamond with high nitrogen content from an Fe3N-C system

The capability of iron nitride, Fe3N for converting graphite to diamond was explored at P = 7 GPa and T = 1550-1850 degreesC in experiments with a duration of 20 h. It was established that depending on the synthesis temperature the iron nitride melt provides conditions for crystallisation of diamond and/or graphite, with the minimal temperature for spontaneous diamond nucleation being approximately 1700 degreesC. Based on the results obtained it was argued that the iron nitride acts as the solvent-catalyst for diamond formation. The crystallised diamonds were found to contain nitrogen in concentration up to approximately 3300 ppm, which depending on the synthesis temperature was present in either the A form or both A and C forms. Absorption peaks caused by hydrogen-related defects were observed in IR spectra of all diamonds examined. For the 3107 cm(-1) line a tendency to increase in intensity with increasing the nitrogen content was found. The well-known blue band-A, N3, H3 and 2.156 eV systems as well as a band with zero-phonon energy at 1.787 eV were observed in cathodoluminescence. (C) 2002 Elsevier Science B.V. All rights reserved.