First-principles Investigation On Mechanical And Electronic Properties Of Carbon Clathrate Structure Materials

High-strength materials have always been an important direction in the field of new materials research due to their irreplaceable important roles in the field of structure and mechanical processing.The new carbon material,clathrate clathrates are fully-sp3 cage-like three dimensional(3D)structures that offer unique mechanical and electronic properties.In this thesis,the mechanical properties of Type-Ⅰ-C46,Type-Ⅱ-C34 and Type-H-C34 carbon clathrates under uniaxial and shear loads are examined by means of ab initio calculations,and in comparison with the experimental and theoretical calculation results of known similar materials.This thesis further constructed the ultralow-density Type-Ⅰ-184,Type-Ⅱ-136 and Type-H-136 large carbon clathrates structures obtained by replacing the carbon atoms in the above three carbon clathrates with carbon tetrahedrons,and investigated their mechanical properties.This thesis first studied the mechanical behavior of the carbon clathrates under uniaxial tension and shear loads.The results showed that their maximum ideal tensile strength exceeds the tensile strength of diamond under<111>direction loads.The maximum ideal shear strength of the carbon clathrates are equivalent to the value of diamond in the(111)<112>direction.This proves the great potential of carbon clathrates as high-strength materials.In addition,this paper also studied the mechanical behavior of the three crystal structures under different loads.It was predicted that those carbon clathrates show distinct anisotropy in their ideal tensile/shear strengths and critical tensile/shear strains,but isotropy in the shear Young’s moduli.Intriguingly,their maximum ideal tensile strengths exceed that of heavyweight diamond under<111>directional load,and their shear Young’s moduli are comparable to that of diamond.Those carbon clathrates show distinct deformability in their critical load-bearing bond configurations,resulting in their distinct mechanical properties.Next,this thesis studied the electrical properties of the three crystal structures subjected to different uniaxial tensile and shear strains.It was found that they are essentially indirect semiconductors,and their electronic properties depend on mechanical strain.The band gap is significantly reduced with increasing strain.This study showed that carbon clathrates can potentially be used as lightweight strong engineering structures and electromechanical equipment.Moreover,the ultra-low-density ternary periodic Ⅰ-184,Ⅱ-136 and H-136 large carbon clathrates structures show unique tensile and shear mechanical properties that greatly vary with the basic carbon cage arrangement and crystallographic orientation.Under uniaxial tension and shear loads,the Ⅱ-136 and H-136 large carbon clathrates exhibit similar anisotropy in the ideal tensile strength,while the Ⅰ-184 type shows isotropy.In addition,the three structures show high tensile/shear toughness,and their densities are extremely low,and they are almost the lightest carbon elemental materials,indicating that they also have broad prospects in engineering applications.