SUPERCRITICAL FLUID SYNTHESIS AND STRUCTURE OF A NEW CUBIC С96 PHASE AS CARBON KFI ZEOLITE WITH sp3/sp2 HYBRIDIZATION

Abstract

The structure of cubic graphite is reinvestigated based on a new electron diffraction experiment and ab initio calculations of carbon zeolites from an available structure database. Carbon micro crystalsassociated with the "cubic graphite" phase were synthesized using the fluid synthesis method at a pressure of up to 200 MPa and a temperature of 500-700 ºС from carbon black as a precursor. According to the results of experiments, methods of experimental electron and X-ray diffractions, as well as ab initio calculations, it is proved that the carbon phase is cubic with lattice parameters ~0.895 nm and space group Im-3m. The crystal structure is proposed as a carbon zeolite with a KFI topology consisting of 96 carbon atoms per unit cell with sp3 hybridization and sp3/sp2 bond types. The hybrid structure is more stable by 0.22 eV per atom. New phase has a density of 2.67 g/cm3 and a high hardness up to 10 GPa.