FORMATION OF CUBIC CARBON BY DYNAMIC SHOCK COMPRESSION OF A DIAMOND AMORPHOUS-CARBON POWDER MIXTURE

A diamond/amorphous carbon powder mixture was shock-compressed by a rod-in-cylinder method. Characterization by high-resolution electron microscopy (HREM) revealed the formation of several carbon modifications. Beside a large amount of graphite, two cubic phases of carbon, turbostratic carbon and chaoite were detected in small quantities. Different phase transition mechanisms were proposed. High temperatures and high pressures in the powder sample resulted in the transformation of amorphous carbon into graphite. One cubic phase corresponded to a modification of diamond (n-diamond) in a previous report determined by observation of the forbidden {200}, {222} and {420} reflections of cubic diamond. We related the presence of these reflections not to cubic diamond, but to a carbon form with a face-centered-cubic (fcc) lattice formed by local melting of the diamond surface and subsequent rapid quenching, and via a solid-vapor-liquid-solid (SVLS) path of phase transitions in amorphous carbon particles. The second cubic phase originated from the deposition of a gaseous or liquid carbon jet on diamond. The lattice parameter was calculated to a(0) = 0.432