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 multi anvil and a Drickamer cell, and the recovered samples were examined by x-ray diffraction and transmission-electron microscopy. Diamond was f ormed in the samples from 14 approximately 20 GPa and 800 approximatel y 1200-degrees-C generated by the multianvil. These P-T conditions are included in the region where the formation of hexagonal diamond was r eported 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 st atic compression was confirmed in the samples from 40 GPa, 25-degrees- C and 14 GPa, 1200-degrees-C.