Since the early days of studies on thermoelectric clathrates it has been evidenced that the lowering of thermal conductivity in these compounds is related to the guest ion's rattling characteristics. Here we report on the relation between the guest vibration and lattice thermal conductivity κL in single crystalline samples of type-I clathrates Ba 8In16Ge30-xMx (M = Si, Sn) with n-type carriers. On going from Mx = Si1.6 to Mx = Sn2.2, the lattice parameter increases by 1% from 11.20 to 11.30 Å. This is accompanied by a decrease from 39 K to 35 K in the local vibration energy of the Ba guest ions in the tetrakaidecahedron cages, and a strong suppression of κL, which shows glasslike temperature dependence for Mx = Sn2.2. We further demonstrate that the lowering of κL at 150 K shows universality behavior and scales very well with the guest free space for vibration in all type-I clathrates, largely independent of the guest or framework ions.
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy