Carbon Clathrates as Strong Lightweight Structures

Abstract Clathrates are fully-sp3 cage-like three dimensional (3D) structures that offer unique mechanical and electronic properties. Here, 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. It is 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 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. Moreover, all investigated carbon clathrates are intrinsically indirect semiconductors, and their electronic properties can be greatly tuned by tension and shear strains. As a consequence, carbon clathrates can be potentially utilized as lightweight strong engineering structures and in electromechanical devices.