Theoretical And Experimental Research On Novel Carbon Structures And Their Properties

In this thesis, the crystal structures and properties of novel carbon allotropes are investigated theoretically and experimentally. Structure search of novel carbon allotropes are performed through CALYPSO and USPEX codes and atom replacement methods based on first principles calculations, and the electronic and mechanical properties are estimated theoretically. The possible synthesis routes and methods are predicted to guiding the experimental synthesis and explain the experimental results. The phase transforms of glassy carbon under high pressure and high temperature achieved on Rockland Research T25 press are investigated. A class of carbons is recovered and the physical, chemical, and mechanical properties are studied.Graphyne polymers, graphdiyne polymers, and yne-diamonds are predicted. Graphyne polymers with different density and tunable electronic properties(e.g., metallic and semiconductive) are constructed because of the diversity of graphyne and the phase transform process. A series of graphdiyne polymers which may coexist are proposed for the complex deformation and bonding of graphdiyne. Graphdiyne polymers are metallic or semiconductive with direct or quasi-direct band gaps. Graphyne and graphdiyne polymers with high hardness, Young’s modulus, and porosity are promising materials in microelectronic devices, energy storage, cutting and grinding, and polishing. Three sp~2 hybridized carbon allotropes with different properties from graphite are predicted. The first carbons are built by parallel staked graphene nanoribbons with the highest energetic stability among three dimensional sp~2 hybridized carbons except graphite. Their tensile behavior is similar to that rubber but different from that of diamond. The largest tensile strain is 13 times that of diamond, and 7 times that of graphene. The second is structured by orthotropic graphene nanoribbons with superconductivity. The synthesis routes of the two carbons are studied. The third is two dimensional carbon allotropes with two-atom thick. They are semiconductive with indirect band gaps.We systematically studied the phase transform mechanism of carbon nanotubes under high pressure. The polymerization is related to the characteristic of nanotubes, including wall numbers, diameters, chiralities, and stacking manners, and pressure state, including hydrostatic and non-hydrostatic pressure. Nanotube polymers show tunable electronic properties, high hardness or superhardness, and high Young’s moduli.Two cubic carbon allotropes are proposed theoretically. The first are constructed by cages with low density and show semiconductive properties. The fcc-C10 shows lowest density similar to that of C60 while the densest fcc-C32 shows comparable density with graphite. The fcc-C32 is superhard with Vickers hardness of 79.9GPa, and fcc-C10 is a ductile material. The second is assembled from carbon triangles showing metallic characteristic for the “bend bond”.A series of novel carbon allotropes with low density, high hardness, high specific strength, and high elastic recovery are synthesized from compressed glassy carbon at high pressure of 25 GPa and high temperature of 400 °C, 600 °C, 800 °C, and 1000 °C. The microstructures of compressed glassy carbon are composed of crossed graphene with sp~2 and sp3 hybridized carbon atoms.