Small-angle X-ray scattering in type Ia diamonds

The results of a small-angle X-ray scattering (SAXS) investigation of natural and synthetic diamonds, with different types of nitrogen-related defects, are presented. They reveal a presence of impurity-rich spherical clusters with a diameter of approximately 90 Angstrom in an IaB diamond. SAXS scattering in an IaA diamond has a much lower intensity, and originates from larger clusters with a considerable variation in size. It is likely that the dominant impurity in these clusters is nitrogen. Present data suggest the possibility that some of the nitrogen-related point defects (A- and B-centers) are not randomly distributed in the diamond lattice, but instead are concentrated in clusters. It is suggested that, although optical manifestations of the A-nitrogen are similar in different diamonds: IaA diamonds can be divided into two sub-groups. The IaA(1) group includes annealed, synthetic, and some natural diamonds. They contain randomly distributed nitrogen pairs, which do not influence mechanical properties and do not produce X-ray scattering. In the IaA(2) group, the diamond aggregation process went further and the formation of nitrogen-containing clusters began. The process of nitrogen aggregation is described in terms of the decay of a supersaturated solid solution of nitrogen in diamond. The driving force for the creation of impurity clusters is the lowering of the free energy of nitrogen dissolution in the diamond lattice, and the decrease of strain. (C) 2000 Elsevier Science S.A. All rights reserved.