First-principles Study Of Formation For Carbide-derived Carbon

The modulus CASTEP of Materials Studio was used in this paper based on densityfunction theory for the study of formation process of SiC-CDC, ZrC-CDC and TiC-CDCby using the first principle of geometry optimization and the first principle of moleculardynamics.The results show that there is a small change on the surface of the derived carbonstructure and no surface reconstruction occured for all of them after the full relaxation,the effects of relaxation are mainly localized on the top two atomic layers, not move intodeeper layers. The surface of these three kinds of derived carbon changes a lot with theremoving of metal atoms layer by layer. After removing the top three atomic layers, the Catoms which on the surface of SiC-CDC and TiC-CDC spread into two layers, but the Catoms are’t spread into layers in ZrC-CDC. C atoms in SiC-CDC drop down and form aneat hexagon eventually, whose vertical view presents plane slice layer structure, whilethe vertical view of ZrC-CDC presents a slight bend curve, the vertical view of TiC-CDCpresents a big wavy shape. It’s known from the analysis of population that the level planeof the three kinds of CDC combined by strong covalent bond, and the vertical direction oflevel plane is decided by weak intermolecular forces. It’s known from the analysis ofenergy band and electronic state density diagrams that the band gap of β-SiC(111) firstdecreases and then increases with the increasing removel layers. Both ZrC(110) andTiC(110) show metalic property, the same as CDC, but with the removel of metalic atoms,the band gap increases and the conductivity decreases. So the layer of removel metalicatoms has strong influence on CDC’s structure and property, and the conductivity of CDCis weaker than that of the carbide.The formation process of SiC-CDC from SiC gradually at the temperature of600,800and900oC show that with the removel of Si atoms layer by layer, Si and C atomsshift to inner and Si atoms relax obviously. The degree of order of the produced SiC-CDCincreases with increasing chlorination temperature, and the microstructure changes fromamorphous carbon to graphite ribbons. It’s known from the analysis of energy band, the band gap of SiC-600first decreases and then increases with the increasing of the removellayer, and the conductivity first increases and then decreases. The microstructure ofSiC-CDC is mostly amorphous carbon at the temperature of600oC, and at thetemperature of800oC exhibits the short chain, when the temperature increasing900oC,there is a chance to obtain the structure of six membered ring although there is no law offormation of honeycomb.