Studies of Small Inclusions in Synthetic Diamonds by Optical Microscopy, Microradiography and Transmission Electron Microscopy

Abstract

A combination of low-resolution and high-resolution techniques was applied to establish the composition, crystallography and distribution of small inclusions, average diameters ~1 [mu]m, dispersed within large synthetic diamonds. Both metallic and silicate phases were present among included bodies, often lying adjacent in the same cavity within the diamond matrix. Monochromatic X-ray microradiography, achieving 1 [mu]m resolution with Cu K[alpha] radiation, demonstrated that transition-metal phases constituted a minor fraction of the total volume of inclusions present. In a specimen rich in dispersed inclusions, the sizes of 1483 inclusions were individually measured. In aggregate they occupied ~4 x 10-4 of the diamond volume. High local inclusion concentrations were associated with high local concentrations of substitutional nitrogen impurity in the diamond matrix. The electron-microscopic techniques included convergent-beam electron diffraction, energy-dispersive X-ray spectroscopy and electron-energy-loss spectroscopy. Detailed crystallographic identifications of individual particles included a b.c.c. Fe-Co alloy (a0 [asymptotically equal to] 2.86 A), a garnet of andradite variety [a0 = 11.95 (5) A] and a clinopyroxene with composition corresponding to that in the augite-ferroaugite division of pyroxenes.