Stability, mechanical and electronic properties of Occ carbon allotropes: Four new tetragonal 3D superhard carbon crystals

Octagonal centered cubic (Occ) carbon allotropes with distinct sp2, and sp3 hybridization have different prop-erties. In this study, four tetragonal novel superhards with mixed sp3-sp2 and all-sp3 hybridization, namely the Occ-C16, Occ-C20, DOcc-alpha C24, and DOcc-beta C24 respectively, which were predicted based on density functional theory. Occ carbon allotropes belong to the P4/mmm (No. 123) space group, their structural and mechanical properties, relative formation enthalpy, calculation of (bulk, shear, Young's) modulus, Vickers hardness, and electronic properties are investigated. These 3D superhards are stable in terms of dynamic and mechanical properties. They also possess a high (bulk, shear, Young's) modulus and Vickers hardness. The predicted B/G ratio for superhards is <1.750, which indicates that Occ carbon allotropes are brittle. In addition, the electronic band structure calculation of Occ-C16 and DOcc-alpha C24 indicates that both are semiconductor superhards with indirect band gaps of 1.710 eV and 1.672 eV, whereas the band structures of Occ-C20 and DOcc-beta C24 show that both superhards are metals. The obtained results show that these four novel superhards can be candidate ma-terials for high-pressure electronic devices.

Automated summary

In this study, four tetragonal novel superhards with distinct sp2, and sp3 hybridization, namely Occ-C16, Occ-C20, DOcc-alpha C24, and DOcc-beta C24 were predicted and investigated. These superhards exhibit stable structural and mechanical properties, high modulus and Vickers hardness. They can be candidate materials for high-pressure electronic devices.