このエントリーをはてなブックマークに追加
ID 19288
file
creator
Takasu, Yuichi
Avila, Marcos A.
abstract
Raman active phonons in the type-I clathrate compounds of X8 Ga16 Ge30 (X=Eu,Sr,Ba) have been fully assigned by the combination of polarized Raman scattering and first principles calculations. The dynamical motions of guest ions in the 6d -site cage have been clearly identified. The energy of the modes, related to a rattling motion, decreases with decreasing temperature. The energy-decrease at low temperatures is a common property for thermal rattling in X8 Ga16 Ge30. The anomalous decreases are originated from the quartic anharmonic potential, and its contribution has been experimentally determined. A mixed state between thermal rattling and quantum tunneling has been observed below 10 K. A soft mode due to the guest ion motion has been observed, but the transition due to this soft mode is somewhat different from the ordinary structural transition because of the shielding by carriers. In addition, it is found that the elastic dispersion of Sr8 Ga16 Ge30 is caused by the interference with the rattling motion of the guest ion in the cage, and that the rattling at the off-center location plays an important role to suppress a lattice thermal conductivity and to achieve the phonon-glass state in X8 Ga16 Ge30.
journal title
Physical Review B - Condensed Matter and Materials Physics
volume
Volume 74
issue
Issue 17
start page
174303-1
end page
174303-5
date of issued
2006-11-22
publisher
American Physical Society
issn
1098-0121
ncid
publisher doi
language
eng
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
publisher
rights
Copyright (c) 2006 The American Physical Society.
relation url
department
Graduate School of Integrated Arts and Sciences
Graduate School of Advanced Sciences of Matter