Authors: P.D. Ownby
Affilation: University of Missouri-Rolla, United States
Pages: 210 - 213
Keywords: diamond 6H polytype, polycrystalline powder, nano crystallites
In 1967, "Hexagonal diamond - a new form of carbon" was reported to be found in meteorites. This hexagonal form, 2H, was named Lonsdaleite, after the noted crystallographer, Kathleen Lonsdale. Since the corrected structures and x-ray diffraction data for all six possible non-cubic polytypes was published in 1992, the considerable increased interest in CVD diamond has resulted in finding other of the predicted polytypes, including 6H, 8H and 15R. The rapid crystallization and cooling characteristics of CVD diamond, and that produced by rapid implosion in meteorites and from man-made explosions, tends to produce non-cubic polytypes because of the rapid and short-lived transformation to the more dense crystal structure. Powder from the latter source has been characterized by infrared spectroscopy, and Rietveld x-ray and neutron diffraction. For particle size fractions in the range of 10 to 1000 nanometers, the non-cubic, 6H hexagonal polytype phase is present in amounts ¡_ 50% and that the cubic diamond phase is present at the ¡Ü 50% level. In all of these size ranges each particle is polycrystalline containing crystallites of nanometer and sub-nanometer dimensions.
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