Negative thermal expansion of fullerite C60 at liquid helium temperatures

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Polycrystalline fullerite Ñ 60 intercalated with Xe atoms at 575 K and a pressure of 200 MPa was studied by powder x-ray diffraction. The integrated intensities of a few brighter reflections have been utilized to evaluate the occupancy of the octahedral interstitial sites in Ñ 60 crystals, which turned out to be (34±4) %, and in good agreement with another independent estimate. It is found that reflections of the (h00) type become observable in Xe-doped Ñ 60 . The presence of xenon in the octahedral sites affects both the orientational phase transition as well as the glassification process, decreasing both characteristic temperatures as well as smearing the phase transition over a greater temperature range. Considerable hysteretic phenomena have been observed close to the phase transition and the glassification temperature. The signs of the two hysteresis loops are opposite. There is reliable evidence that at lowest temperatures studied the thermal expansion of the doped crystal is negative under cool-down.

Section: Resultsmentioning

confidence: 99%

Hysteretic phenomena in Xe-doped C60 from x-ray diffraction

Prokhvatilov

Galtsov

Legchenkova

et al. 2005

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“…Since the discovery of the fullerite molecule C 60 [1], the low-temperature physical properties of fullerite C 60 have been investigated by various methods: inelastic neutron scattering [2,3], infrared and Raman spectroscopy [4,5], x-ray [3,6,7], neutron [8] and electron [9,10] diffraction, NMR [11], dilatometry [12][13][14][15] and calorimetry [16][17][18][19][20][21][22][23][24][25]. It has found that fullerite C 60 is a molecular crystal in which the molecules are bonded by the van der Waals forces and its physical properties are largely determined by the dynamics of the rotational motion of the C 60 molecules.…”

Section: Introductionmentioning

confidence: 99%

The low-temperature heat capacity of fullerite C60

Bagatskii

Sumarokov

Barabashko

et al. 2015

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PostprintThis is the accepted version of a paper published in Low temperature physics (Woodbury, N.Y., Print). This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Bagatskii, M., Sumarokov, V., Barabashko, M., Dolbin, A V., Sundqvist, B. (2015) The low-temperature heat capacity of fullerite C 60 . Abstract:The heat capacity at constant pressure of fullerite C 60 has been investigated using an adiabatic calorimeter in a temperature range from 1.2 to 120 K. Our results and literature data have been analyzed in a temperature interval from 0.2 to 300 K. The contributions of the intramolecular and lattice vibrations into the heat capacity of C 60 have been separated. The contribution of the intramolecular vibration becomes significant above 50 K. Below 2.3 K the experimental temperature dependence of the heat capacity of C 60 is described by linear and cubic terms. The limiting Debye temperature at T → 0 K has been estimated (Θ 0 = 84.4 K). In the interval from 1.2 to 30 K the experimental curve of the heat capacity of C 60 describes the contributions of rotational tunnel levels, translational vibrations (in the Debye model with Θ 0 = 84.4 K), and librations (in the Einstein model with Θ E,lib = 32.5 K). It is shown that the experimental temperature dependences of heat capacity and thermal expansion are proportional in the region from 5 to 60 K. The contribution of the cooperative processes of orientational disordering becomes appreciable above 180 K. In the high-temperature phase the lattice heat capacity at constant volume is close to 4.5 R, which corresponds to the hightemperature limit of translational vibrations (3 R) and the near-free rotational motion of C 60 molecules (1.5 R).

“…The measurements were made in the interval 2.2-43 K using a low temperature capacitance dilatometer with a sensitivity of 0.02 nm. The dilatometer design and the measuring technique are detailed in [19]. Prior to measurement, the cell with the sample of pressure-oriented SWNTs was evacuated at room temperature for 72 h to remove possible gas impurities.…”

Section: Experimental Techniquementioning

confidence: 99%

Low-temperature radial thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen

Долбин

Esel'son

Gavrilko

et al. 2010

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The effect of a N 2 impurity on the radial thermal expansion coefficient α r of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2-43 K by the dilatometric method. Saturation of nanotube bundles with N 2 caused a sharp increase in the positive magnitudes of α r in the whole temperature range used and a very high and wide maximum in the thermal expansion coefficient α r (T) at T ~ 28 K. The lowtemperature desorption of the impurity from the N 2 -saturated powder of bundles of single-walled carbon nanotubes with open and closed ends has been investigated. PACS: 65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems; 81.07.De Nanotubes.