Newly Designed 3D Carbon Allotrope with High Hardness and Strong UV-Vis Light Absorption

Designing cage-based three-dimensional (3D) carbon allotropes is of significant interest due to their unique chemical and physical properties, along with fascinating applications in nanoelectronics, optoelectronics, and nanomechanics. Among the many studied carbon polymorphs, however, it is urgent to find 3D-ordered porous architectures with high hardness, mechanical strength, and thermal stability as an alternative to the expensive diamond. Therefore, motivated by the synthesis of the V-carbon, we design a new superhard 3D monoclinic carbon structure (dubbed 3D m-C-16) in which all carbon atoms are coordinated through sp(3)-hybridized bonding in 5-, 6-, and 7-membered rings. Its optimized structure exhibits excellent dynamic, mechanical, and thermal stability. Unlike the small direct band gap with a semiconducting nature in Z-ACA carbon, the porous 3D m-C-16 shows a wide indirect band gap with an insulating nature and high cohesive energy. Also, the computed mechanical properties of this system are comparable to those found in V-carbon and diamond. Equally important, they carry anisotropic elasticity, high refractive index, excellent UV-Vis light absorption, and strong phonon inelastic scattering. Our study expands the cage-based 5-6-7 carbon rings family with new features.