Thermal conductivity of Xe clathrate hydrate at low temperatures

The effective thermal conductivity of the powder samples of xenon hydrate was measured in the interval 2-170 K using the steady-state method. The thermal conductivity of the homogeneous Xe clathrate hydrate was estimated from the effective thermal conductivity using an empirical expression. The applicability of the formula was checked by comparing two powder samples with different grain size and porosity. The temperature dependence of the thermal conductivity kappa(T)similar to T (n) of Xe clathrate hydrate is divided into four distinct temperature regimes (I-IV) with different n. In the interval 55-97 K (III) the behavior of kappa(T) shows an anomaly, where the thermal conductivity decreases by almost 50% as the temperature increases. This observation is attributed to the resonant scattering where the coupling of the lattice with "rattling" motions of Xe atom dominates the thermal resistivity at high temperature. Since the observed vibrational energy of Xe in the small cages is similar to 4 meV (or approximate to 46 K) the resonant scattering contribution to the thermal resistivity is expected to decrease in an interval of comparable temperature. The thermal conductivity in the low temperature regime (regimes I and II) is found to follow the prediction of the soft-potential model. The data on thermal conductivities of several gas clathrate hydrates are compared.