  Clathrates are lightweight, cage-like, fully-sp3 three dimensional (3D)
structures that are experimentally-available for several host elements of the
IV group. However, carbon clathrates are as yet hypothetical structures.
Herein, the mechanical properties of Type-I-C46 Type-II-C34 and Type-H-C34
carbon clathrates are explored by first-principles calculations. It is revealed
that those carbon clathrates show distinct anisotropic patterns in ideal
tensile/shear strengths and critical tensile/shear strains, with maximum ideal
tensile strength of Type-I carbon clathrate that is superior over that of
diamond in <111> direction. However, it is identified isotropy in shear Youngs
modulus, and in terms of tensile/shear Youngs moduli, they are sorted as Type-I
> Type-II > Type-H carbon clathrates. There are distinct critical load-bearing
bond configurations that explain their distinct mechanical behaviors. Moreover,
those carbon clathrates are intrinsically indirect semiconductors, and their
electronic properties can be greatly dictated by mechanical strain. Carbon
clathrates can be potentially utilized as lightweight technically robust
engineering metastructures and in electromechanical devices.
