LINEAR FINITE CARBON CHAINS (CARBYNES) - THEIR ROLE DURING DYNAMIC TRANSFORMATION OF GRAPHITE TO DIAMOND, AND THEIR GEOMETRIC AND ELECTRONIC-STRUCTURE

Linear carbon allotropes (carbynes) with sp sigma-hybridizations may play a role as precursors and mediating structures during shock-induced transformation of graphite to diamond in the presence of a high-temperature pulse. There is some evidence that carbynes are thermodynamically stable (polytypic) allotropes of carbon at very high temperatures, and that they will be formed by bond-splitting within the planar graphite layers. Earlier suggestions by Heimann et al. (Carbon, 22 (2) (1984) 147) to explain the conformation of carbynes by kinking of carbon chains with cumulated double (cumulene) and conjugated triple (polyyne) bonds can be supported by the concept by Rice et al. (Phys. Rev. B, 34 (6) (1986) 4139) of strong intrinsic electron-phonon coupling in infinite and finite polyyne (carbyne) chains that is being expressed through the occurrence of solitons and, in doped material, by polarons.