Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

Abstract

For the first time the linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles at low temperatures (2.2–120 K). The measurements were performed using a dilatometer with a sensitivity of 2·10⁻⁹ cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5–30 μm. The change of sign of the radial thermal expansion coefficient at 5.5 K was observed.