The coefficients of thermal expansion (13 to 139 OK), heat capacity (2 to 20°K), andvelocity of longitudinal and transversal ultrasonic waves (88 to 190 OK) for solid CO, have been determined along the solid-vapour equilibrium line. Heat capacity of constant volume, adiabatic and isothermal compressibilities, the Griineisen and Poisson coefficients were calculated using the above data. The contributions of various types of heat motion to heat capacity, thermal expansion and compressibility have been separated, and the parameters of isolated orientational defects in crystalline CO, determined. The connection between the orientational defect parameters and the extent of non-centricity of intermolecular interactions in solids is discussed.Die thermischen Ausdehnungskoeffizienten (13 bis 139 OK), die Wiirmekapazitiit (2 bis 20 "K) und die longitudinale und transversale Ultraschallgeschwindigkeit (88 bis 190°K) wurden fur festes CO, ander Festkorper-Dampf-Gleichgewichtslinie bestimmt. Mit den erhaltenen Werten wurden die Wirmekapazitit bei konstantem Volumen, die adiabatischen und isothermen Kompressibilititen und die Griineisen-und Poissonkoeffizienten berechnet. Die Beitriige verschiedener Arten der Wirmebewegung zur Wirme-. kapazitiit, thermischen Ausdehnung und Kompressibilitiit wurden separiert und die Parameter von isolierten Orientierungsdefekten in kristallinem CO, bestimmt. Die Verbindung zwischen den Parametern der Orientierungsdefekte und dem AusmaD der Nichtzentrizitit von intermolekularen Wechselwirkungen in Festkorpern wird diskutiert.

A simple adiabatic calorimeter has been made to investigate the heat capacity of small samples (≤ 1 cm 3 ) of carbon nanomaterials in the temperature range from 1 to 300 K. It makes possible: i) short-time mounting of a sample; ii) doping of samples with gases directly in the calorimeter; iii) short-time cooling of a sample down to helium temperatures. The adiabatic calorimeter is suitable to place into a helium vessel of a portable Dewar or a helium cryostat. The heat capacity of the fullerit sample has been measured in the temperature range from 1 to 30 K. PACS: 81.05.U-Carbon/carbon-based materials; 65.40.Ba Heat capacity.

The specific heat at constant pressure C(T) of bundles of single-walled carbon nanotubes (SWNTs) closed at their ends has been investigated in a temperature interval of 2 -120 K. It is found that the curve C(T) has features near 5 K, 36 K, 80 K and 100 K. The experimental results on the C(T) and the radial thermal expansion coefficient  R (T) of bundles of SWNTs oriented perpendicular to the sample axis have been compared. It is found that the curves C(T) and  R (T) exhibit a similar temperature behavior at T>10 K. The temperature dependence of the Gruneisen coefficient (Т) has been calculated. The curve (Т) also has a feature near 36 K. Above 36 K the Gruneisen coefficient is practically independent of temperature (4). Below 36 K (Т) decreases monotonically with lowering temperature and becomes negative at T< 6 K. PACS: 65.40.Ba Heat capacity; 65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems; 81.07.De Nanotubes.

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The heat capacity of orientationally disordered solid solutions (CH4)nKr1−n (n=75 and 78 mole% CH4 in the temperature interval ΔT=0.8–20 K) and (CD4)nKr1−n (n=50, 60, and 70 mole% CD4, ΔT=0.6–30 K) is investigated. At liquid-helium temperatures the temperature dependences of the molar heat capacities of the rotational subsystems of the solutions are qualitatively and quantitatively very different. One of the main reasons for the effect is that in the concentrated solutions investigated the CD4 molecules are in a substantially stronger molecular field than the CH4 molecules. This is because in low-energy states the effective octupole electric moment of CD4 molecules, which determines the molecular field, is larger than the effective octupole moment of the more quantum molecules CH4. The weak concentration dependences of the heat capacity of the solutions studied are due to the influence of frustration, which weakens the molecular fields produced at the lattice sites by the surrounding molecules. No evidence of the formation of orientational octupole glasses in the experimental systems was found.

The heat capacity of Kr–nCH4 solid solutions with the concentrations n=1; 5; 10% and of the solid solution Kr–1% CH4–0.2% O2 is studied at 0.7–8 K. The contributions Crot to the heat capacity of the solutions due to the rotation of the CH4 molecules are estimated. The deviations of the measured Crot from the values corresponding to the equilibrium distribution of the CH4 nuclear spin modifications are dependent on the correlation between the characteristic times of conversion and of the calorimetric experiment. The effects of temperature, O2 impurities, and CH4 clusters upon the conversion rate are studied. It is shown that the hybrid mechanism of conversion proposed by Berlinsky and Nijman, which takes into account both intramolecular and intermolecular interactions of the proton spins, is predominant.

Low-temperature heat capacity of cryocrystals, which contain impurity clusters has been investigated theoretically and experimentally. Such defects might essentially enrich low-frequency part of the phonon spectrum by introducing both localized and delocalized vibrations. The effect of both types of the vibrations on the temperature dependence of the heat capacity is analyzed. Heat capacity of the disordered solid solution Kr-Ar (Ar concentration is~25%) is studied as an example of the effect of the light weakly connected impurities on the low-temperature thermodynamic characteristics of the system. The mass defect of such an impurity induces «phonon pumping» from the low-frequency part of the spectrum into the high-frequency part and decreasing the low-temperature heat capacity, while the weakened interaction between the impurity and the host atoms combined with even weaker interaction between the impurities leads to the formation of the low-temperature maximum on the heat capacity temperature dependence. The analysis performed shows that at rather high Ar concentrations, the nonmonotonous temperature dependence of the relative change in the heat capacity of solid Kr Ar 1-p p solutions is determined by excitation of delocalized high-dispersion low-frequency phonons. PACS: 63.20.-e Phonons in crystal lattice; 63.20.Mt Phonon-defect interaction; 63.50.+x Vibrational states of disordered systems; 63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions.

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