Computational Prediction of a Novel Superhard sp 3 Trigonal Carbon Allotrope with Bandgap Larger than Diamond

Searching for new carbon allotropes with superior properties has been a longstanding interest in material sciences and condensed matter physics. Here we identify a novel superhard carbon phase with an 18-atom trigonal unit cell in a full-sp (3) bonding network, termed tri-C-18 carbon, by first-principles calculations. Its structural stability has been verified by total energy, phonon spectra, elastic constants, and molecular dynamics simulations. Furthermore, tri-C-18 carbon has a high bulk modulus of 400 GPa and Vickers hardness of 79.0 GPa, comparable to those of diamond. Meanwhile, the simulated x-ray diffraction pattern of tri-C-18 carbon matches well with the previously unexplained diffraction peaks found in chimney soot, indicating the possible presence of tri-C-18 carbon. Remarkably, electronic band structure calculations reveal that tri-C-18 carbon has a wide indirect bandgap of 6.32 eV, larger than that of cubic diamond, indicating its great potential in electronic or optoelectronic devices working in the deep ultraviolet region.

Automated summary

The study identified and verified a new superhard carbon phase, tri-C-18 carbon, with high bulk modulus and Vickers hardness, as well as potential applications in deep ultraviolet electronic or optoelectronic devices based on its electronic band structure.