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The isochoric thermal conductivity of Kr₀.₆₃Xe₀.₃₇ solid solution has been investigated for three samples with different molar volumes in the temperature range from 80 K to the onset of melting, as well as the thermal conductivity of the ternary (Kr₀.₆₃Ar₀.₁₈₅Xe₀.₁₈₅) and quaternary (Kr₀.₆₃Ar₀.₁₂Xe₀.₁₂(CH₄)0.₁₃) solid solutions. It is found that for multi-component alloys, the thermal conductivity reaches a minimum, whereby adding more impurity atoms in the solid solution does not affect the thermal conductivity in agreement with the recent nonequilibrium molecular dynamics calculations for argon. The phonon contribution to the total thermal conductivity depends significantly on molar volume of sample and impurity concentration, in contrast to the contribution of diffusive modes, which is practically independent of these factors. Досліджено ізохорну теплопровідність твердого розчину Kr₀.₆₃Xe₀.₃₇ для трьох зразків з різними молярними об’ємами в інтервалі температур від 80 К до початку плавлення, а також теплопровідність потрійного (Kr₀.₆₃Ar₀.₁₈₅Xe₀.₁₈₅) та чотирьохкомпонентного (Kr₀.₆₃Ar₀.₁₂Xe₀.₁₂(CH₄)0.₁₃) твердих розчинів. Виявлено, що для багатокомпонентних розчинів теплопровідність досягає мінімуму, в результаті чого подальше додавання домішкових атомів в твердий розчин не впливає на теплопровідність відповідно до недавніх розрахунків з використанням методів нерівноважної молекулярної динаміки (NEMD) для аргону. Фононний внесок в теплопровідність істотно залежить від молярного об’єму зразка та концентрації домішки, на відміну від вкладу дифузних мод, який практично не залежить від цих чинників Исследована изохорная теплопроводность твердого раствора Kr₀.₆₃Xe₀.₃₇ для трех образцов с разными молярными объемами в интервале температур от 80 К до начала плавления, а также теплопроводность тройного (Kr₀.₆₃Ar₀.₁₈₅Xe₀.₁₈₅) и четырехкомпонентного (Kr₀.₆₃Ar₀.₁₂Xe₀.₁₂(CH₄)0.₁₃) твердых растворов. Обнаружено, что для многокомпонентных растворов теплопроводность достигает минимума, в результате чего дальнейшее добавление примесных атомов в твердый раствор не влияет на теплопроводность в соответствии с недавними расчетами с использованием методов неравновесной молекулярной динамики (NEMD) для аргона. Фононный вклад в теплопроводность существенно зависит от молярного объема образца и концентрации примеси, в отличие от вклада диффузных мод, который практически не зависит от этих факторов.

Thermal conductivity of solid furan has been measured at isochoric conditions in the high-temperature orien-tationally-disordered phase I for samples of different densities. Our isochoric data show a gradual increase of ΛV with temperature whereas isobaric thermal conductivity goes down in this temperature range. The above effect is most clearly expressed in furan, where the atoms in the ring plane are not equivalent, as compared with earlier studied C₆H₆ and C₆H₁₂. The increase of ΛV with temperature can be attributed to weakening of the translation-al-orientational interaction which, in turn, leads to a decrease of phonon scattering on rotational excitations. The experimental data are described in terms of a modified Debye model of thermal conductivity with allowance for heat transfer by both low-frequency phonons and ―diffuse‖ modes.

The isochoric thermal conductivity of solid n-hexane C6H14 is studied using three samples with different densities for temperatures ranging from 100 K to the onset of melting. In all cases, the isochoric thermal conductivity varies more weakly than Λ∝1/T. The present results are compared with the thermal conductivities of other representatives of the n-alkanes. The contributions of low-frequency phonons and “diffuse modes” to the thermal conductivity are calculated.

The isochoric thermal conductivity of gama-O2 has been studied on samples of varying density in the temperature interval from 44 K to the onset of melting. The thermal conductivity of nearly free sample decreases at rising temperature along the isochores. It is shown that the absolute value of thermal conductivity in the gama-phase of O2 is close to its lower limit and most of the heat is transported by "diffusive" modes. The growth of thermal conductivity in gama-O2 is attributed to the decay of the phonon scattering at the rotational excitations of the molecules and at the short-range magnetic order fluctuations at rising temperature., Comment: Postscript 9 pages, 2 figures, 1 table. To be published in 2005

The isochoric thermal conductivity of (CH4)1−ξKrξ solid solutions is studied between 40 K and ∼150 K over a wide range of concentrations (ξ=0.013, 0.032, 0.07, 0.115, 0.34, 0.71, 0.855, 0.937, and 0.97). A gradual transition from the thermal conductivity of a highly perfect crystal to the minimum thermal conductivity is observed as the crystal becomes increasingly more disordered. A qualitative description is given in the framework of Debye model of thermal conductivity, which takes into consideration the fact that phonon mean free path cannot decrease indefinitely.

The isochoric thermal conductivity of solid propane C3H8 is investigated on three samples of different densities in the temperature interval from 50K to the onset of melting. In all cases the isochoric thermal conductivity exhibits dependences that are weaker than Λ∝1∕T. The results obtained are compared with those for other representatives of n-alkanes. The experimental data are discussed within a model in which the heat is transported by low-frequency phonons and by “diffusive” modes above the phonon mobility edge.

Thermal conductivity of solid cyclopentane C5H10 has been measured at isochoric conditions in the plastic phases I and II for samples of different densities. Isochoric thermal conductivity is nearly constant in phase II and increases with temperature in phase I. Such behaviour is attributed to weakening of the translational orientational coupling which, in turn, leads to a decrease of phonon scattering on rotational excitations. The experimental data are described in terms of a modified Debye model of thermal conductivity with allowance for heat transfer by both low-frequency phonons and diffusive modes.

The isochoric thermal conductivity of solid trifluoromethane was investigated for three samples of different densities in the interval from 75 K to the onset of melting. The isochoric thermal conductivity first decreases with increasing temperature, passes through a minimum at T ~ 100 K, and then starts to increase slowly. The results obtained are compared with the thermal conductivities of other freons of methane series. The correlation between the temperature dependence of isochoric thermal conductivity and the character of the rotational molecular motion is discussed.

The isochoric thermal conductivity of solid nitrogen has been investigated on four samples of different densities in the temperature interval from 20 K to the onset of melting. In alfa-N2 the isochoric thermal conductivity exhibits a dependence weaker than 1/T; in beta-N2 it increases slightly with temperature. The experimental results are discussed within a model in which the heat is transported by low-frequency phonons or by "diffusive" modes above the mobility boundary. The growth of the thermal conductivity in beta-N2 is attributed to the decreasing "rotational" component of the total thermal resistance, which occurs as the rotational correlations between the neighboring molecules become weaker., Postscript 12 pages, 3 figures, 1 table. To be published in 2005

The isochoric thermal conductivities of the solid solutions (CO2)0.905Kr0.095 and (CO2)1−xXex (x=0.052 and 0.097) of different densities are investigated in the temperature interval from 150K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO2 at T>150K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of CO2∕Kr and CO2∕Xe solid solutions first decreases, passing through a minimum at 200–210K, and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO2 molecules, which gain more freedom as the spherically symmetrical inert gas atoms are dissolved in the CO2.