Low-temperature heat capacity of fullerite C60 doped with deuteromethane

Abstract

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 ...

The low-temperature heat capacity of fullerite C60

“…Note that the data on the heat capacity of C 60 are essential for analyzing the heat capacities of new C 60 -containing nanomaterials, for example, elementary atomic and molecular gaseous substances that form interstitial solutions in the octahedral voids of fullerite C60 [39][40][41].…”

Low-temperature dynamics of matrix isolated methane molecules in fullerite C60: The heat capacity, isotope effects

“…(1). The dependences s CH4 (T) and s CD4 (T) 13 for the solutions (CH 4 ) 0.40 C 60 and (CD 4 ) 0.40 C 60 are illustrated in Fig. 4.…”

“…4. The characteristic conversion times s CH4 (T) (᭺) and s CD4 (T) 13 (solid line) of CH 4 and CD 4 molecules in the octahedral cavities of fullerite.…”

“…It is found that the impurity molecules have a minor effect on the motion of the molecules C 60 . The CH 4 molecules execute rotational vibrations at helium temperatures and a weakly hindered rotation at T $ 120 K. 6 The heat capacity of the solution (CD 4 )0.40C 60 in the temperature interval 1.2-120 K was measured by Bagatskii et al 13 The results of analysis of the rotational-vibrational states of the CD 4 molecules in the octahedral cavities in fullerite C 60 13 are in good agreement with the inelastic neutron scattering 6 and NMR spectroscopic 2,3 data on the dynamics of the molecular motion in the solutions (CH 4 ) 0.92 C 60 and (CD 4 ) 0.88 C 60 .…”

“…13 Intercalation of fullerite with CH 4 and CD 4 molecules (and other simple impurities [14][15][16][17][18][19][20][21][22][23] ) leaves the structures of the high-temperature and low-temperature phases of fullerite unaltered. The lattice parameters of the high-temperature phase of the solutions (CH 4 ) 0.91 C 60 and (CD 4 ) 0.87 C 60 increase at T % 300 K by 0.026 and 0.016 Å , respectively, 2,6 relative to that of pure C 60 (a ¼ 14.161 Å (Ref.…”