Radial thermal expansion of pure and Xe-saturated bundles of single-walled carbon nanotubes at low temperatures

TL;DR

This study measures the low-temperature radial thermal expansion of pure and Xe-saturated single-walled carbon nanotube bundles, revealing negative expansion at very low temperatures and significant effects due to Xe doping.

Contribution

It provides new experimental data on the thermal expansion behavior of nanotube bundles, highlighting the impact of Xe saturation and temperature-dependent expansion features.

Findings

Individual nanotubes exhibit negative thermal expansion.

Xe doping increases the magnitude of expansion and introduces a peak around 50-65 K.

Xe concentration affects the peak without altering low-temperature expansion outside the peak.

Abstract

The radial thermal expansion coefficient (a)r of pure and Xe-saturated bundles of single-walled carbon nanotubes has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low temperature capacitance dilatometer with a sensitivity of 2x10-9 cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid compacted material has a positive expansion coefficient due to expansion of the intertube volume in the bundles. Doping the nanotubes with Xe caused a sharp increase in the magnitude of (a)r in the whole range of temperatures used, and a peak in the dependence (a)r (T) in the interval 50-65 K. A subsequent decrease in the Xe concentration lowered the peak considerably but had little effect on the thermal expansion coefficient of the sample outside the region of the peak. The features revealed have been explained qualitatively.