Microstructure of nanocrystalline diamond powders studied by powder diffractometry

Abstract

High resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from 5 to 250nm were analyzed and provided information on grain structure, average size of crystallites, and concentration of dislocations. Selected samples were heat treated at 1670K at pressures 2.0 and 5.5GPa or had surface modified by outgassing, heat treatment at vacuum conditions, and by controlled adsorption of gases. The apparent lattice parameter method was applied to characterize the structure of a shell-core model of nanosize particles. The multiple whole profile fitting provided information on crystallite sizes and density of dislocations. Population of dislocations increased with applied pressure, while strain and interplanar distances in the surface layers decreased. Adsorption of foreign gases on the grain surface modified the structure of the surface layers but did not affect dislocations near the center of the grains.

Surface graphitization of ozone-treated detonation nanodiamonds

“…A previous report indicated that even a weak oxygen concentration can accelerate the graphitization kinetics of detonation NDs and affects the nature of sp 2 ‐induced structures . A similar catalytic effect of oxygen was proposed for graphitization of diamond crystals . Oxygen may promote a new route for diamond conversion into sp 2 forms .…”

Vacuum or flowing argon: What is the best synthesis atmosphere for nanodiamond-derived carbon onions for supercapacitor electrodes?

“…Different synthesis atmospheres may also differ in the amount of gases containing reactive oxygen from the atmosphere or desorbing from the precursor. The catalytic effect of oxygen decreases the onset of graphitization and increases the graphitization rate, which may lead to different carbon nanostructures [50][51][52].…”

Nanocrystalline materials studied by powder diffraction line profile analysis

“…However, it was observed for 5 nm grain size diamond powders that the broadening of peak profiles is resulted rather by the small crystallite size and the stacking faults and not by dislocations, see Fig. 17 [112]. Assuming a shell-core model of the diamond nanoparticles, the defect structure of the internal region and the shell strains were obtained from the line broadening and the diffraction vector dependence of the apparent lattice parameter, respectively [112][113][114].…”