STRUCTURAL TRANSFORMATIONS OF THE CUMULENE FORM OF AMORPHOUS CARBYNE AT HIGH-PRESSURE

Structural transformations of the cumulene form of amorphous carbyne w hich are induced by heating at high pressure (7.7 GPa) are investigate d. These can be described by the sequence amorphous phase crystal - am orphous phase - disordered graphite. Raman scattering shows that predo minately the chain structure of carbyne remains at the first three sta ges, It was found that the intermediate crystalline phase is an unknow n modification of carbon whose structure is identified as cubic (a = 3 .145 Angstrom). A mechanism of structural transformations in carbyne t hat involves the formation of new covalent bonds between chains is dis cussed. (C) 1997 American Institute of Physics.