Dynamical motion of a guest ion studied by Raman scattering and the lattice thermal conductivity in A 8 Ga 16 Si 30−x Ge x (A = Ba, Sr)
ABSTRACT Dynamical motions of a guest ion in type-I clathrate compounds have been investigated using Raman scattering. It has been found that the 4th order anharmonic potential is important for the guest ion motion not only for A8Ga16Ge30 (A = Ba, Sr, Eu), but also for A8Ga16Si30-xGex (A = Ba, Sr). The substitution of Ge expands isotropically the cage at 6d-site for Ba8Ga16Si30-xGex, however, anisotropically for Sr8Ga16Si30-xGex. Especially, for Sr8Ga16Si30-xGex, the off-center rattling develops with increasing Ge concentration and plays an important role to the suppression of the lattice thermal conductivity.