Glass-like behaviour of thermal conductivity of CH4-CD4 solid solutions

Some mixed crystals show a low-temperature thermal-conductivity dependence on temperature similar to that of amorphous solids. This phenomenon is usually ascribed to a disorder of another kind. In the current paper we report results of measurements of the thermal conductivity of CH4 - CD4 solid solution which also displays a glass-like behaviour for some concentrations of deuterated methane. Here, however, the disorder appearing at these concentrations of CD4 cannot account for the characteristic plateau. Instead, we explain it in terms of an enhancement of the phonon-rotation interaction resulting from lowering the symmetry of the molecular field.