To investigate the off-center rattling motion and its charge-carrier dependence in type-I clathrate compounds, we carried out ultrasonic measurements on type-I Ba 8Ga 16Sn 30 and a reference compound, K 8Ga 8Sn 38. We found elastic softening of C 44 originating from a lattice instability due to the off-center rattling motion of Ba atom in Ba 8Ga 16Sn 30. Elastic softening below 1 K suggests that the lattice instability remains at very low temperatures. We also found ultrasonic dispersion which has no mode selectivity. No-mode-selective ultrasonic dispersion in Ba 8Ga 16Sn 30 would be caused by a strong electron-phonon coupling. No charge-carrier dependence is observed between n-type and p-type Ba 8Ga 16Sn 30. The significant softening on the bulk modulus in Ba 8Ga 16Sn 30 contrasts to the continuous hardening in K 8Ga 8Sn 38, indicating the central role of the rattling motion in the softening.
|Physical Review B - Condensed Matter and Materials Physics
|Published - Feb 7 2012
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics