Phase transitions of carbon nanotube bundles under non-proportional triaxial compressions

Lateral compressions of (n, n) and (n, 0) single-walled carbon nanotube (SWCNT) bundles are simulated by density functional theory. Feasible transition pathways are verified by the body-centered tetragonal C-4 (bct-C-4) phase from the (4, 4) bundle and the carbon-centered orthorhombic C-8 (Cco-C-8) phase from (6, 6) and (8, 8) bundles. Three new phases, the sp(3)-hybridized phases Cco-C-16 from the (4, 0) bundle and Cco-C-32 from the (8, 0) bundle, the hexagonal phase Hex-C-24 composed of sp(2)- and sp(3)-hybridized carbons from the (6, 0) bundle, under non-proportional triaxial loading are predicted. Measured hardness values for Cco-C-16/C-32 exceed 40 GPa, indicating super-hardness. Electronic band structures of Cco-C-16/C-32 exhibit a 3.64 eV bandgap, while Hex-C-24 exhibits metallic carbon properties. Our results provide the potential phase transition pathways of SWCNT bundles under non-proportional compression.

Automated summary

In this study, the phase transition pathways of single-walled carbon nanotube (SWCNT) bundles under lateral compression are investigated using density functional theory. Several new phases of carbon nanotubes are discovered, and their properties are predicted. The findings have important implications for understanding the phase transition behavior of carbon nanotubes.