No abstract

The isochoric thermal conductivity of γ-O 2 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 γ-phase of O 2 is close to its lower limit and most of the heat is transported by «diffusive» modes. The growth of thermal conductivity in γ-O 2 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.

The thermal conductivity of solid ethane (C2H6) is investigated for three samples of different density in the temperature range from 35K to the onset of melting. In all cases the isochoric thermal conductivity in the α and β phases decreases with increasing temperature by a dependence weaker than Λ∝1∕T. Such behavior is typical for orientationally ordered phases of molecular crystals and does not reveal any clear features due to rotation of the methyl groups. The thermal conductivities of ethane and some of its halogen derivatives (freons) are compared. The experimental results are discussed in the framework of a model in which heat is transported by low-frequency phonons, and, above the mobility edge, by high-frequency “diffusive” modes.