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Results of the small-angle X-ray scattering (SAXS) of diamonds with different concentrations and types of optically-active defects are reviewed. It is shown that nitrogen-free (IIA) diamonds and diamonds with a low degree of nitrogen aggregation have no SAXS. Annealing of diamonds leads to the formation of three-dimensional clusters of defects with sizes in the range from ~8 to 60 nm. There is no correlation between nitrogen concentration and the existence or the size of the clusters, however, the clusters are related to the degree of diamond annealing. The presence of the clusters is unrelated to 'platelets' and they contain little, if any, nitrogen. With annealing, the size of the clusters decreases and the contrast of electronic density with the matrix increases.

Hardening of fullerite C 60 during temperature-induced polymerization and amorphization under pressure Mechanical properties ͑Vicker's hardness, Young's modulus, and fracture toughness coefficient͒ have been studied for the three-dimensionally polymerized, amorphous, and nanocrystalline diamond-plus-graphite composite carbon phases prepared from fullerite C 60 by temperature treatment under pressure. The hardness was found to increase gradually with the synthesis temperature. The experimental values of hardness are well correlated with the density of samples regardless of the phase structural nature, displaying the same dependence as amorphous carbon films. It has been shown that the hardness and Young's modulus of both polymerized crystalline and disordered phases, though not as high as those of diamond, are comparable to the properties of cubic BN, while fracture toughness coefficient can be higher than that for diamond. An unusual combination of high hardness and high plasticity has been established for strongly polymerized C 60 .

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