Theoretical Design And Experimental Research Of Novel Carbon With Sp Hybrids

In this thesis,the novel carbons containing sp-hybrid are investigated from both theoretical design and experimental exploration.CALYPSO code based on first-principle was used to search the new carbons,and the mechanical and electrical properties are calculated using the CASTEP module in the Materials Studio,VASP and Quantum-ESPRESSO software based on the density functional theory.Using vacuum sintering,high temperature and high pressure methods?cubic high pressure apparatus and Rockland Research T-25 press?,pure graphdiyne is used as raw material to explore the phase transitions.A new sp-sp² hybridized carbon allotrope,namely Tetra-carbon,is predicted through the evolutionary particle swarm structural search and CASTEP module.Tetra-carbon has a 3D framework composed of sp² carbon helixes connected by linear sp carbon chains,similar to the interconnected network of propadienyl groups,which forms the well-proportioned microporous structure.Tetra-carbon is thermodynamically more stable than known graphdiyne and carbyne carbon,and also shows mechanical and dynamic stabilities at ambient pressure.Tetra-carbon is a semiconductor with an indirect band gap of 3.27 eV,and has anisotropic tensile strengths with an unexpected large tensile strain of0.64 along the[001]direction.Base on the analysis of B/G and Poisson's ratios as well as the tensile strains,it is significantly revealed that Tetra-carbon is a mechanically ductile microporous carbon allotrope.We reveal the mystery of an enchanting carbon allotrope with sp-,sp²-,and sp³-hybridized carbon atoms using a newly developed ab initio particle-swarm optimization algorithm for crystal structure prediction.This crystalline allotrope,namely m-C₁₂,can be viewed as braided mesh architecture interwoven with multigraphene and carbon chains.The ground-state energy,independent elastic constant,and phonon dispersion spectra calculations confirm that the structure is thermodynamically,mechanically,and dynamically stable.Based on the unique structural features of m-C₁₂,as well as the band structure,the electronic contributions of different atoms to the Fermi surface,and the projected density of states,we found that m-C₁₂is superconducting with a superconducting transition temperature Tc of 1.13 K.In addition,analysis of the B/G and Poisson's ratio indicates that this allotrope is ductile.Based upon the first-principles calculations,two new three-dimensional?3D?microporous carbon allotropes consisting of whorl chains and connected by consecutive double bonds in sp-sp² bonding networks have been proposed in this work.One of these structures,namely the Trig-C₉,was obtained by the evolutionary particle swarm structural search,while the other called the Trig-C₁₅was obtained by inserting double bonds in the Trig-C₉.Both the 3D sp-sp² hybridized carbons have a trigonal structure with 9 and 15 atoms in the hexagonal primitive cells.The calculated results demonstrate that these polymorphs are thermodynamically,mechanically,and dynamically feasible.The Trig-C₉and Trig-C₁₅are indirect semiconductors with band gaps of 2.70 eV and 1.25 eV,respectively.Their unique frameworks render them mechanical ductility and obvious elastic anisotropy.Graphdiyne as raw material was sintered in a vacuum sintering furnace to investigate the phase transition.With the temperature increasing,it was found that graphdiyne could have been transformed into new phase and the transforming temperatures are 600°C,1100°C and 1400°C,respectively.Graphdiyne has been shown to undergo graphitization at temperatures of 800°C,1400°C,and 1600°C under 5GPa on cubic high pressure apparatus.Graphdiyne has been transformed to graphite-like structures by sintering under10 GPa,12GPa and 15 GPa at 1000°C on a large volume press;graphdiyne was transformed into diamond-like structure under 15 GPa at 1200°C;graphdiyne may be transformed to diamond-15 R structure under 15 GPa at 1900°C;graphdiyne may have undergone a new phase change sinstered at 15 GPa 800°C and 25 GPa 800°C,which needs further experimental verification.