Dynamical motions of the guest ions in type-I clathrates Sr8Ga16Si30-xGex and Ba8Ga16Si30-xGex have been studied by Raman scattering spectroscopy, to clarify the role of guest vibration modes in these systems with unusual thermal transport behaviors. An anomalous decrease of the guest energies with decreasing temperature is observed for both systems. The Ge-doping expands the cage surrounding the 6d site anisotropically for Sr8Ga16Si30-xGex, but isotropically for Ba8Ga16Si30-xGex. Especially for Sr8Ga16Si30-xGex, off-center rattling arises simultaneously with the anisotropic expansion, and it is confirmed that these anomalies play a crucial role to suppress lattice thermal conductivity in these systems.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)