Glass-like thermal transport in symmetry-broken clathrates

We present the quantitative interpretation for the glass-like behavior of thermal conductivities k(T) for type-I clathrate compounds involving off-centered guest ions. It is shown that the dipole-dipole interaction generated in cage/guest-ion systems is crucial to reproduce the characteristics of thermal conductivities for these symmetry-broken clathrates. The above scenario also explains well the difference of.(T) between the p-type and the n-type beta-BGS found recently by K. Suekuni et al. (Phys. Rev. B, 77 (2008) 235119.) Copyright (C) EPLA, 2009