The nitrogen aggregation sequence and the formation of voidites in diamond

High-temperature annealing of type IaB diamonds containing platelets caused the conversion of the platelets to dislocation loops and the formation of octahedral shaped defects [T. Evans, I. Kiflawi, W. Luyten, G. Van Tendeloo , G.S. Woods, Proc. R. Sec. Lend. A 449 (1995) 295]. The chemical compositi on of these octahedral defects was investigated, and they were found to con tain molecular nitrogen, thus showing them to be the same as the voidite de fects observed in natural diamonds. This demonstrates the last stage of the sequence of the aggregation of nitrogen in diamonds. The amount of nitroge n in the 'manmade' voidites was found to be similar to the amount of nitrog en in the platelets before their conversion to dislocation loops. Also, a p ossible mechanism for the formation of B centres From A centres is discusse d. (C) 2000 Published by Elsevier Science S.A. All rights reserved.