Computational Prediction of a Novel Superhard sp 3 Trigonal Carbon Allotrope with Bandgap Larger than DiamondSupported by the National Natural Science Foundation of China (Grant Nos. 11804307, U1804155, and U1604263), and the China Postdoctoral Science Foundation (Grant Nos. 2018M630830 and 2019T120631).

Abstract

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-C18 carbon, by first-principles calculations. Its structural stability has been verified by total energy, phonon spectra, elastic constants, and molecular dynamics simulations. Furthermore, tri-C18 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-C18 carbon matches well with the previously unexplained diffraction peaks found in chimney soot, indicating the possible presence of tri-C18 carbon. Remarkably, electronic band structure calculations reveal that tri-C18 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.