High-temperature high-pressure annealing of diamond - Small-angle X-ray scattering and optical study

Annealing of Ib and IIa diamonds at temperature of 1800degreesC and pressure of 7.2 GPa was performed. It is shown that for experiments with comparable total duration, the nitrogen aggregation rate is significantly slower for a single-run than for multiple-run annealing. Consequently, many previously reported multiple annealing experiments could overestimate the rate of nitrogen diffusion in diamond. Small-angle X-ray scattering reveals that three-dimensional defect clusters were formed during annealing, The size of clusters (27-57 nm) is similar in annealed natural IaA, IaB, IIa and synthetic Ib diamonds. The presence of clusters is unrelated to 'platelets' and contain little, if any, nitrogen. Optical results reveal that annealing resulted in decay of the 4N-2V (H4) defects into 2N-V (H3) and that the B nitrogen defect is not responsible for the N9 optical center. (C) 2001 Elsevier Science B.V. All rights reserved.