A superhard and superdense carbon allotrope with all-sp3 bonded helical chains of five-membered rings

Abstract

Superhard materials have garnered considerable attention in diverse fields including machinery, petrochemicals, and high-pressure science. Carbon is always a promising candidate for the development of novel superhard materials with superior characteristics, such as superdensity, exceeding that of diamond, and excellent physical properties. However, the progress in the discovery of superhard and superdense carbon has been limited. Here, we propose a novel sp³-bonded superhard and superdense carbon allotrope named T-C₁₀. The thermal, energetic, dynamical and mechanical stabilities of T-C₁₀ were confirmed by employing ab initio molecular dynamics, cohesive energy, phonon frequencies and elasticity constant calculations, respectively. The Vickers hardness of T-C₁₀ is 90 GPa according to Gao's model, which is close to that of diamond. Electronic structure and mechanical property calculations indicate that T-C₁₀ is semiconductive with an indirect band gap of 4.62 eV, and exhibits impressive mechanical properties such as notable uniaxial tensile strength and incompressibility along the z-axis direction and salient elastic anisotropies. Additionally, the outstanding optical absorption in the ultraviolet region endows T-C₁₀ with potential as a material for ultraviolet absorbers and storage.