Thermal expansion of single-walled carbon nanotube (SWNT) bundles: X-ray diffraction studies

Abstract

Thermal expansion coefficient in single-walled carbon nanotube bundles was determined as $(\ensuremath{-}0.15\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} (1/\mathrm{K})$ for the tube diameter and $(0.75\ifmmode\pm\else\textpm\fi{}0.25)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} (1/\mathrm{K})$ for the triangular lattice constant by means of x-ray scattering between 300 K to 950 K. The value for the intertube gap was $(4.2\ifmmode\pm\else\textpm\fi{}1.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} (1/\mathrm{K}),$ which is larger than $2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5} (1/\mathrm{K})$ for the c-axis thermal expansion in graphite. The results reveal the presence of a remarkably larger lattice anharmonicity in nanotube bundles than that of graphite. The small value for the tube diameter is consistent with the seamless tube structure formed by a strong covalent bond between carbon atoms comparable to that in graphite.