A. I. Krivchikov

Thermal Conductivity of Methane-Hydrate

The thermal conductivity of the methane hydrate CH4 (5.75H2O) was measured in the interval 2–140 K using the steady-state technique. The thermal conductivity corresponding to a homogeneous substance was calculated from the measured effective thermal conductivity obtained in the experiment. The temperature dependence of the thermal conductivity is typical for the thermal conductivity of amorphous solids. It is shown that after separation of the hydrate into ice and methane, at 240 K, the thermal conductivity of the ice exhibits a dependence typical of heavily deformed fine-grain polycrystal. The reason for the glass-like behavior in the thermal conductivity of clathrate compounds has been discussed. The experimental results can be interpreted within the phenomenological soft-potential model with two fitting parameters.

Thermal conductivity of solid krypton with methane admixture

The thermal conductivity of CH4–Kr solid solutions is investigated at CH4 concentrations 0.2–5.0% in the temperature range 1.8–40 K. It is found that the temperature dependence of the thermal conductivity has features typical of resonance phonon scattering. The analysis of the experimental results shows that the main contribution to the impurity-caused scattering of phonons is made by the scattering on rotational excitations of the nuclear spin T-species of CH4 molecules. The phonon–rotation interaction parameter is estimated.

Thermal conductivity of tetrahydrofuran hydrate

The thermal conductivity of tetrahydrofuran hydrate has been measured in the temperature region 2-220 K by the steady-state potentiometric method. The temperature dependence of the thermal conductivity exhibits behavior typical of amorphous substances. It is shown that above 100 K the mean free path of the phonons is considerably smaller than the lattice parameter and is no longer dependent on temperature.

Experimental evidence of the role of quasilocalized phonons in the thermal conductivity of simple alcohols in orientationally ordered crystalline phases

The thermal conductivity κ(T) of crystalline alcohols (methyl, ethyl and 1-propyl) within their thermodynamic equilibrium phases for T⩾2K and under the equilibrium vapor pressures has been measured and analyzed. While such compounds usually exhibit a rich polymorphism including amorphous and partially ordered crystals, the phases here explored correspond to crystals showing complete orientational order. The results show that the temperature dependence of κ(T) above its maximum deviates from the expected 1∕T-law decrease with increasing temperature, arising from anharmonic interactions involving acoustic excitations. Such a deviation is here attributed to the presence of a component κII(T) corresponding to the shortest-lifetime phonons (Cahill-Pohl model), in addition to the component κI(T) related to propagating phonons and thus: κ(T)=κI(T)+κII(T). Above T=40K, κI(T) does follow the 1∕T law and κII(T) is basically temperature independent. The component κI(T) is well described by the Debye-Peierls model ta...

Deuteration effects in the thermal conductivity of molecular glasses

The thermal conductivity κ(T) of pure deuterated ethanol has been measured at the equilibrium vapor pressure of its orientationally-ordered crystal form (T = 2 K − Tm), orientational glass, and glass state (T = 2 K − Tg, Tg is the glass transition temperature) solid phases. The temperature dependence of the conductivity is well described by the sum of two contributions, κ(T) = κI(T) + κII(T), where κI(T) accounts for heat transport by acoustic phonons and κII(T), for heat transfer by localized high-frequency excitations. The thermal conductivities of deuterated and hydrogenated ethanols are compared in the different phases. The mechanisms of phonon scattering in the glasses are analyzed. In these glasses the effect of complete deuteration shows up in the κII(T) term.

Anisotropy of the Thermal Conductivity of Parahydrogen Crystals

The anisotropy of thermal conductivity of parahydrogen crystals has been observed for the first time. The thermal conductivity measurements have been made on samples of different diameters at the temperature range from 2 to 8 K.

Low-temperature properties of monoalcohol glasses and crystals

We discuss our work on simple aliphatic glass-forming monoalcohols at low temperatures, including experiments on specific heat, thermal conductivity, Brillouin scattering and x-ray diffraction. The family of simple monoalcohols is an interesting model system for exploring molecular glass-forming liquids, the low-temperature universal properties of glasses, and even the glass transition phenomenon itself. More specifically, we examine the role of the molecular aspect ratio in the kinetics of vitrification/crystallization, the reported appearance of particular cases of polymorphism (in ethanol) and polyamorphism (in butanol), and, especially, the influence of positional isomerism and the location of the hydrogen bond on the lattice dynamics and, therefore, on the universal low-temperature properties of glasses.

Heat transfer in solid methyl alcohol

The thermal conductivity coefficient κ(T) is measured under equilibrium vapor pressure for two crystalline phases of pure methanol (orientationally ordered and orientationally disordered) at temperatures from 2K to the melting temperature Tm and also for a CH3OH+6.6% H2O glass from 2K to the glass transition temperature Tg and in the supercooled liquid from Tg to 120K. The dependence κ(T) is described approximately as a sum of two contributions: κI(T), describing heat transport by acoustic phonons, and κII(T)—by localized high-frequency excitations. The temperature dependences of the thermal conductivity of primary monoatomic alcohols CH3OH, C2H5OH, and C3H7OH in the glass state are compared. Different mechanisms of phonon scattering in the crystalline phases and glass are analyzed. The κII(T) contribution is calculated within the Cahill–Pohl model. There is an anomaly of the thermal conductivity of the glass state near Tg (a smeared minimum on the κ(T) curve).The thermal conductivity coefficient κ(T) is measured under equilibrium vapor pressure for two crystalline phases of pure methanol (orientationally ordered and orientationally disordered) at temperatures from 2K to the melting temperature Tm and also for a CH3OH+6.6% H2O glass from 2K to the glass transition temperature Tg and in the supercooled liquid from Tg to 120K. The dependence κ(T) is described approximately as a sum of two contributions: κI(T), describing heat transport by acoustic phonons, and κII(T)—by localized high-frequency excitations. The temperature dependences of the thermal conductivity of primary monoatomic alcohols CH3OH, C2H5OH, and C3H7OH in the glass state are compared. Different mechanisms of phonon scattering in the crystalline phases and glass are analyzed. The κII(T) contribution is calculated within the Cahill–Pohl model. There is an anomaly of the thermal conductivity of the glass state near Tg (a smeared minimum on the κ(T) curve).

Heat transfer in crystalline clathrate hydrates at low temperatures

The experimental results on the thermal conductivity κ(T) of crystalline Xe, CH4, and THF clathrate hydrates are analyzed. In a wide region of temperatures above 2K, κ(T) exhibits a behavior typical of disordered solids, which depends weakly on their chemical composition, crystalline structure, and microstructure. The results are discussed in the context of phenomenological models of phonon scattering by local modes. It is found that the Xe clathrate has a feature unusual for glasses, namely, κ(T) decreases almost two-fold as the temperature increases from 50 to 100K. The behavior of κ(T) is presumably determined mainly by the strong phonon scattering on water molecules.

Heat Transfer in Solid Solutions Hydrogen-Deuterium

The thermal conductivity of parahydrogen-orthodeuterium solid solutions with the orthodeuterium concentration of 0.01 to 100% has been investigated in the temperature range from 1.8 K to the melting point. The experimental data have been analyzed in terms of the Callaway model. It has been found that the intensity of phonon scattering by isolated orthodeuterium impurities in solid hydrogen is much higher than that in classical crystals. The impurity additional scattering of phonons has been supposed to be due to variations in force constants and lattice distortions in the vicinity of impurity molecules in quantum crystals. The above effects have been quantitatively estimated. The concentration dependences of the thermal conductivity and phonon scattering intensity have been considered.