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

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.

Anisotropic Optical, Mechanical, and Thermoelectric Properties of Two-Dimensional Fullerene Networks

“…A band gap of 1.55 eV is found in α-C 60 -2D, which is relatively consistent with the experimental value of 1.66 eV, revealing the mid-band gap semiconductor properties. Generally, the carbon allotropes possess band gaps in excess of 2 eV and tend to exhibit insulating properties, such as diamond, V-carbon, W-carbon, M-carbon, Cco-C 8 , Bct-C 4 , T-carbon, and penta-graphene. ,− Compared to the typical carbon allotropes with wider band gaps, the fullerenes connected by bridging covalent bonds as studied in this work form a semiconductor α-C 60 -2D with a moderate band gap. Both experimental and theoretical results reveal that the band gap of α-C 60 -2D is not far from the cubic silicon .…”

Newly Designed 3D Carbon Allotrope with High Hardness and Strong UV–Vis Light Absorption

“…Figure a shows that the predicted porous 3D m -C 16 is an insulator with a wide indirect band gap of 5.428 eV. The computed value of the band gap is larger than those of the 3D tetrahexcarbon (3D th -C 12 ) (3.92 eV), V -carbon (4.48 eV), and diamond (5.4 eV) at the HSE06 level, while it is less than those of 3D C 20 T (5.44 eV) and trigonal carbon (3D tri -C 18 ) (6.32 eV), as listed in Table . The wide band gap of the 3D m -C 16 , which can be due to the sp 3 -hybridization of C atoms from different carbon rings (5-, 6-, and 7- rings), highly suggests its numerous applications in electronics.…”

“…The ductility and brittleness of the material can be identified by defining its Pugh’s ratio ( K / G ). , A material is ductile only if K / G is higher than 1.75; otherwise, it is brittle. The calculated value of the Pugh’s ratio of the monoclinic 3D m -C 16 is 0.858, suggesting its higher brittleness nature compared with the 3D th -C 12 , tri -C 18 , C 20 T carbon, and simple cubic carbon ( sc -C 22 ), as presented in Table , but as compared to diamond, the porous 3D m -C 16 is more ductile due to its unique cage-based 5–6–7-memebred carbon rings.…”

Pressure-induced phase transition in transition metal trifluorides

“…Ab initio calculations The search for TiF 3 structures (1-4 formula units) was performed at pressures of 20 GPa and 50 GPa via an unbiased swarm intelligence based method, Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO), [44][45][46] which is designed to search for the most stable or metastable structures of given compounds. [47][48][49][50][51][52][53][54][55][56][57] Our first-principle calculations were based on density functional theory, [58] as implemented in the VASP package. [59] The core electrons were treated by the projector-augmented wave approximation, [60] and the exchange-correlation functional was given by the generalized gradient approximation parameterized by Perdew, Burke, and Ernzerhof.…”