On the effective Debye temperatures of the C60 fullerite

The effective Debye temperatures Theta(eff) determined for solids by different physical methods have been analyzed and compared. Attention has been focused on the original parameter of the Debye theory of heat capacity, i.e., the translational calorimetric Debye temperature Theta(t)(c) (0), and the X-ray Debye temperature Theta(x) in the framework of the Debye-Waller theory for the C-60 fullerite. It has been established that the true Debye law T-3 is satisfied for the C-60 fullerite over a very narrow range of temperatures: 0.4 K <= T <= 1.8 K. For this reason, the experimental Debye temperatures Theta(t)(c) (0) obtained for the C-60 fullerite by different authors in the range T > 4.2 K are characterized by a large scatter (by a factor of similar to 5). It has been revealed that the value Theta(t)(c) (0) = 77.12 K calculated in this paper with the use of the six-term Betts formula from the harmonic elastic constants (C) over tilde (ijkl) of the C-60 single crystal in the limit T = 0 K is closest to the true Debye temperature. It has been demonstrated using the method of equivalent moments that the real spectral frequency distribution of translational lattice vibrations g(omega) for the C-60 fullerite deviates from a parabolic distribution. The effective Debye temperatures Theta(eff) involved in applied problems of thermodynamics of crystals and elastic scattering of different radiations from lattice vibrations have been determined. The quantitative measure of anharmonicity of translational and librational lattice vibrations of the C-60 fullerite has been determined. This has made it possible to empirically evaluate the lattice thermal conductivity kappa of the C-60 fullerite at T approximate to 300 K: kappa(300) = 0.80 W (m/K), which is in good agreement with the experimental thermal conductivity kappa(exp) = 0.78 W (m/K) at T approximate to 250 K.