The formation and annealing of paramagnetic defects in high-pressure and high-temperature diamond were investigated via a heat-treatment study of as-grown crystals. The crystals were subjected to isochronal annealing at 1550 to 2000C, and the concentrations of paramagnetic defects were determined by performing electron paramagnetic resonance measurements after each annealing step. The quantitative data were analyzed in terms of recent results on the behavior of Ni and/or N defects during annealing. Like the P1 and W8 centers, the NIRIM1 Ni-related defects exhibited a strong decrease in their concentration upon annealing at 1900C, whereas the NIRIM2 centers seemed to be rather stable. The evolution of the Ni-related center concentration during the annealing sequence showed that not all of the W8 defects transformed into paramagnetic Ni–N complexes. Most of the W8 defects were transformed into other non-paramagnetic centers, and the AB1, AB3 and AB6 defects were suggested to be by-products of this process. The relatively low concentrations of Ni–N paramagnetic complexes which formed during annealing showed that their formation did not play any fundamental role in the kinetics of N aggregation during heat treatment.

The Effect of High-Pressure–High-Temperature Annealing on Paramagnetic Defects in Diamond. R.N.Pereira, W.Gehlhoff, A.J.Neves, N.A.Sobolev, L.Rino, H.Kanda: Journal of Physics - Condensed Matter, 2003, 15[39], S2941-9