An annealing study was made of the paramagnetic defects found in synthetic diamond grown from Ni solvent/catalysts. The substitutional N0 and Ni- defects exhibited a similar behavior during annealing at 1550 to 2000C. New paramagnetic centers (AB6, AB7) became detectable upon annealing. The AB5 center was found to appear in as-grown high-pressure high-temperature material which was rich in N, and its concentration decreased with increasing annealing temperature. The AB1, AB3, AB6 and AB7 defects were produced in the early stages of annealing, and were suppressed by heating to above 1900C. Possible origins of the AB paramagnetic centers were considered in the light of

recently proposed mechanisms of N aggregation and Ni–N complex formation in high-pressure high-temperature diamond.

Annealing Study of the Formation of Nickel-Related Paramagnetic Defects in Diamond. R.N.Pereira, A.J.Neves, W.Gehlhoff, N.A.Sobolev, L.Rino, H.Kanda: Diamond and Related Materials, 2002, 11[3-6], 623-6