A study was made of the point defects which were detectable in as-grown and annealed synthetic diamonds by using electron paramagnetic resonance and infra-red spectroscopy. The specimens were grown by using a temperature-gradient method, using Fe-Ni-C or Fe-Co-C solvent catalysts, at 1700K and 5.5GPa. The first observations were reported of the N-vacancy (W15) and W33 electron paramagnetic resonance centres in as-grown and annealed Ni- and Co-containing samples. The generation of interstitials and vacancies occurred during the transformation of substitutional Ni into the NE4 defect, which had the structure of a double semi-vacancy. This transformation and its reverse, plus the existence of differing charge states of Ni and N defects, explained the aggregation of N at low annealing temperatures. Most of the Nis- was transformed into Ni-N complexes at 1600 to 1900K. The N aggregation which was observed at higher annealing temperatures was attributed to a third mechanism which involved an enhancement of the Ni mobility; due to the Coulomb field of negatively charged Ni-containing centres. The charge transfer which was induced by X-irradiation indicated the existence of nearest-neighbour N-N+ and separated N pairs, N---N+. A decreasing content of neutral and positive N charge states, which occurred upon X-irradiation, was attributed to charge transfer between Nis-, P1, A-centres and separated P1 pairs.

Mechanisms of Nitrogen Aggregation in Nickel- and Cobalt-Containing Synthetic Diamonds. V.A.Nadolinny, A.P.Yelisseyev, J.M.Baker, D.J.Twitchen, M.E.Newton, B.N.Feigelson, O.P.Yuryeva: Diamond and Related Materials, 2000, 9[3-6], 883-6