We report on thermoelectric and Raman scattering studies of single crystalline samples of a type I clathrate Ba 8Ga 16Sn 30. The n- and p-type samples have a thermopower of -300 μV/K and +270 μV/K, and electrical resistivity of 20 mΩ cm and 40 mΩ cm at room temperature, respectively. Regardless of the charge carrier type, the lattice thermal conductivity κ L shows typical glass-like behavior. The low-energy vibration of Ba(2) in the tetrakaidecahedron is manifested in the Raman scattering spectrum as a peak at 15 cm -1. This energy agrees with the characteristic vibrational temperature of 20 K derived from the analysis of the specific heat data with a soft-potential model. The fact that both the vibrational energy and the magnitude of κ L for Ba 8Ga 16Sn 30 are lowest among the type I clathrates is evidence that off-center vibrations are responsible for the strong reduction of κ L. Analysis of κ L(T) revealed that the positional disorder associated with the off-center vibrations acts as the Rayleigh scattering center, and the coupling between guest vibrational modes and acoustic phonons is stronger than that in Sr 8Ga 16Ge 30 and Eu 8Ga 16Ge 30.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry