V.V. Sumarokov1, A. Jeżowski2, D. Szewczyk2, M.I. Bagatski1, M.S. Barabashko1,3, A.N. Ponomarev4, V.L. Kuznetsov5,6, and S.I. Moseenkov5
1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
2W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences P.O. Box 1410, Wroclaw 50–950, Poland
3National Research Tomsk Polytechnic University, 30 Lenin Ave., Tomsk 634050, Russia
4Institute of Strength Physics and Materials Science of SB RAS, 2/4 Academicheskii Ave., Tomsk 634055, Russia
5Boreskov Institute of Catalysis, 5 Lavrentiev Ave., Novosibirsk 630090, Russia
6National Research Tomsk State University, 36 Lenin Ave., Tomsk 634050, Russia
Received December 17, 2018
The specific heat of multi-walled carbon nanotubes (MWCNTs) with a low defectiveness and with a low content of inorganic impurities has been measured in the temperature range from 1.8 to 275 K by the thermal relaxation method. The elemental composition and morphology of the MWCNTs were determined using scanning electron microscopy analysis and energy dispersion x-ray spectroscopy. The MWCNTs were prepared by chemical catalytic vapor deposition and have mean diameters from 7 nm up to 18 nm and lengths in some tens of microns. MWCNTs purity is over 99.4 at.%. The mass of the samples ranged from 2–4 mg. It was found that the temperature dependence of the specific heat of the MWCNTs differs significantly from other carbon materials (graphene, bundles of SWCNTs, graphite, diamond) at low temperatures. The specific heat of MWCNTs systematically decreases with increasing diameter of the tubes at low temperatures. The character of the temperature dependence of the specific heat of the MWCNTs with different diameters demonstrates the manifestation of different dimensions from 1D to 3D, depending on the temperature regions. The crossover temperatures are about 6 and 40 K. In the vicinity of these temperatures, a hysteresis is observed.
Key words: carbon nanotubes, MWCNTs, specific heat, low-dimensional systems.