X-RAY-DIFFRACTION AND TRANSMISSION-ELECTRON MICROSCOPY OF NATURAL POLYCRYSTALLINE GRAPHITE RECOVERED FROM HIGH-PRESSURE

Natural polycrystalline graphite was compressed using a 6-8-type multianvil and a Drickamer cell, and the recovered samples were examined by x-ray diffraction and transmission-electron microscopy. Diamond was formed in the samples from 14 approximately 20 GPa and 800 approximately 1200-degrees-C generated by the multianvil. These P-T conditions are included in the region where the formation of hexagonal diamond was reported by Bundy and Kasper. Hexagonal diamond was not apparent in any of the recovered samples. Instead, the formation of n-diamond, which is a new carbon phase recently identified in a shock-wave study, by static compression was confirmed in the samples from 40 GPa, 25-degrees-C and 14 GPa, 1200-degrees-C.