New carbon allotropes in sp + sp$^3$ bonding networks consisting of C$_8$ cubes

TL;DR

This paper reports the discovery of new three-dimensional carbon allotropes with C8 cube structures, featuring mixed sp and sp3 bonding, which are energetically favorable and exhibit semiconducting properties with significant band gaps.

Contribution

The study introduces novel C8 cube-based carbon allotropes with mixed bonding, expanding the known structural diversity and electronic characteristics of carbon materials.

Findings

New C8 cube-based carbon structures identified

These allotropes are more stable than linear carbyne and diamond forms

They exhibit semiconducting behavior with band gaps of 3.08 eV and 2.53 eV

Abstract

We identify by ab initio calculations a new type of three-dimensional carbon allotropes constructed by inserting acetylenic or diacetylenic bonds into a body-centered cubic C$_8$ lattice. The resulting $sp+sp^3$-hybridized cubane-yne and cubane-diyne structures consisting of C$_8$ cubes can be characterized as a cubic crystalline modification of linear carbon chains, but energetically more favorable than the simplest linear carbyne chain and the cubic tetrahedral diamond and yne-diamond consisting of C$_4$ tetrahedrons. Electronic band calculations indicate that these new carbon allotropes are semiconductors with an indirect band gap of 3.08 eV for cubane-yne and 2.53 eV for cubane-diyne. The present results establish a new type of carbon phases consisting of C$_8$ cubes and offer insights into their outstanding structural and electronic properties.