MECHANISMS OF PHONON-SCATTERING IN LAYERED CLAYS

The thermal conductivity at 2-200 K, both in-plane and out-of-plane, a nd heat capacity at 4-80 K of layered vermiculite have been measured. Our experimental data have been analyzed together with the thermal con ductivity data for muscovite and phlogopite (from literature), taking into account the peculiarities of the lattice dynamics of the complex layered materials. The low-lying optical modes play an important role both for the heat capacity at T > 20 K and the phonon scattering. The main mechanisms of phonon scattering at the lowest temperatures are fo und to be the boundaries and the structure defects. The defects give a quadratic frequency dependence of the inverse relaxation time; such a dependence may be explained by the peculiar displacement-distance rel ation for point defects in layered structures.