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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., Dolbin, A., Sundqvist, B. (2012) Low-temperature heat capacity of fullerite C-60 doped with deuteromethane.Low temperature physics (Woodbury, N.Y., Print) The heat capacity C of fullerite doped with deuteromethane (CD 4 ) 0.4 (C 60 ) has been investigated in the temperature interval 1.2 -120 K. The contribution 4 CD ΔC of the CD 4 molecules to the heat capacity C has been separated. It is shown that at T ≈ 120 K the rotational motion of CD 4 molecules in the octahedral cavities of the C 60 lattice is weakly hindered. As the temperature decreases to 80 K, the rotational motion of the CD 4 molecules changes from weakly hindered rotation to libration. In the range T = 1. Keywords:Heat capacity, fullerite С 60 , rotational dynamics of CD 4 IntroductionThe discovery of new forms of carbon (fullerite, carbon nanotubes, graphene) has attracted much interest from researchers working in different fields of physics, chemistry and materials science. The interest is first of all provoked by the wide-range diversity of the physical and chemical properties of these objects. A comprehensive investigation of the physical properties of these materials is of great importance for both fundamental science and practical applications.The thermal properties of pure fullerite have been investigated in numerous studies. Unfortunately, there have been few studies of the dynamics of impurities in C 60 crystals.In the low temperature phase there is one octahedral and two tetrahedral cavities for each C 60 molecule in the lattice. The average sizes of these are ≈ 4.12 Ǻ and ≈ 2.2 Ǻ, respectively [1,2]. Under certain conditions the octahedral cavities can be occupied by impurity atoms or molecules whose sizes are smaller than or similar to the size of the cavity. By now various experimental methods have been used to investigate fullerite C 60 doped with inert gas atoms [3][4][5][6][7][8] and simple molecules [9][10][11][12][13][14][15] of different symmetries and sizes. Doping affects significantly the physical properties of fullerite at low temperatures [16][17][18].The quantitative and qualitative features of the behavior of A x C 60 (A = 4 He, Ne, Ar, Kr, Xe) and M x C 60 (M = H 2 , N 2 , O 2 , CO, CH 4 , CD 4 ) systems depend in particular on the concentration x (x is the fraction of the octahedral cavities occupied by admixtures) and on the atomic / molecular parameters of the admixtures. Note that in a 4 He -C 60 solution the 4 He atoms can also occupy the tetrahedral cavities. The masses, the moments of inertia, the central and noncentral forces of the pair interaction of H 2 , N 2 , O 2 , CO, CH 4 and CD 4 molecules are much smaller than those of C 60 molecules. As a result, admixture of these molecules to fullerite ...

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“…This term is sensitive to even low impurity concentrations [23,25]. The impurities randomly distributed in the crystal generate random deformation fields leading to higher stochastization of tunnel levels [50,51].…”

Section: Resultsmentioning

confidence: 99%

The low-temperature heat capacity of fullerite C60

Bagatskii

¹

,

Sumarokov

²

,

Barabashko

³

et al. 2015

Low Temperature Physics

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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).

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“…It should be noted that such a crystal field is responsible for the low-temperature zero-pressure thermodynamics of classical ͑cubic͒ rare-gas solids doped with rotor molecules. 12 We also address here the problem of the second-harmonic crystal field components. In particular, we take into account one of the anisotropic interactions that has been ignored in the previous theories of the S 0 (0) band structure.…”

Section: Introductionmentioning

confidence: 99%

Low-frequency Raman excitations in phase I of solidH2:Role of crystal fields

Goncharov

¹

,

Strzhemechny

²

,

Mao

³

et al. 2001

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Low-frequency Raman spectra ͑up to 800 cm Ϫ1 ) measured below 18 K are reported for the entire pressure range of phase I of para-hydrogen doped with low fractions of the ortho-modification. In addition to bands corresponding to the E 2g optical phonon and the Jϭ2←0 rotational transitions, we observed a weak band attributed as S 0 (1). These spectra are employed to deduce information on the interactions that play a decisive role in bringing about the transition to the broken symmetry phase II. A new theoretical analysis is presented to understand the rotational Raman excitations and the role of various pairwise anisotropic interactions between H 2 molecules. In order to explain the pressure dependence of the S 0 (0) and S 0 (1) bands, we infer that a fourth-harmonic crystal field is present. The frequencies of the S 0 (0) and S 0 (1) bands are used to reconstruct the respective crystal field parameter.

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Cited by 10 publications

References 7 publications

Low-temperature heat capacity of fullerite C60 doped with deuteromethane

Low-temperature heat capacity of fullerite C60 doped with deuteromethane

The low-temperature heat capacity of fullerite C60

Low-frequency Raman excitations in phase I of solidH2:Role of crystal fields

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