Extremely high tensile strength and superior thermal conductivity of an sp3-hybridized superhard C24 fullerene crystal

Abstract

Low-dimensional carbon allotropes could be used as fundamental building blocks to bottom-up build new materials with excellent properties. In this study, a lightweight sp³-hybridized carbon allotrope named 3d-C₂₄ is suggested to be obtained by polymerizing fullerene C₂₄ molecules. By means of first-principles density functional theory (DFT) calculations, 3d-C₂₄ is confirmed to be not only dynamically and thermodynamically but also mechanically stable. Quasiharmonic calculations show that 3d-C₂₄ has a quite low thermal expansion coefficient at room temperature and exhibits superior high-temperature dynamic stability even up to 2700 K. Although 3d-C₂₄ is a lightweight carbon material, it has a very high Vickers hardness which is even higher than that of superhard cubic BN. The weak anharmonicity in bonding results in an abnormally low Grüneisen parameter at room temperature. Its tensile strength is extremely high and even superior to that of diamond in the [111] direction. Electronic structure calculations reveal that 3d-C₂₄ is a semiconductor with an indirect bandgap of 3.65 eV. Anharmonic DFT calculations confirm that 3d-C₂₄ has a very high thermal conductivity. In addition, infrared and Raman spectra are also investigated which could be used as a fingerprint to identify 3d-C₂₄ from other carbon allotropes.