Designing a sp3 structure of carbon T-C9: First-principles calculations

Abstract

A novel superhard carbon allotrope T-C9 with an all-sp3 bonding network is theoretically predicted in this work. The new phase of the carbon allotrope has tetragonal symmetry with space group P-4m2, and the structural properties, stability, mechanical anisotropy, mechanical and electronic properties of T-C9 are systematically investigated utilizing density functional theory. T-C9 is mechanically and dynamically stable, and T-C9 is favorable in energy which is lower than T carbon by 0.459 eV/atom at zero pressure. The bulk modulus and shear modulus of T-C9 are calculated to be 328 GPa and 243 GPa, respectively, which are slightly larger than those of T-C5, mC12 and tP40 carbon. The brittleness and superhardness of T-C9 are confirmed by the values of B/G (1.35) and the hardness (66.7 GPa), respectively. In addition, the ratio of the maximum and minimum Young's modulus reveals that T-C9 exhibits anisotropy, especially in the (110) and (111) directions. Electronic properties indicate that T-C9 can be considered to be semiconductor material with a wide indirect band gap of 4.128 eV.

Keywords

• Carbon allotrope
• Superhard
• Anisotropy
• Wider band gap