Off-center rattling and anisotropic expansion of type-I clathrates studied by Raman scattering.
Dynamical motions of the guest ions in type-I clathrates Sr8Ga16Si(30-x)Gex and Ba8Ga16Si(30-x)Gex 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 Sr8Ga16Si(30-x)Gex, but isotropically for Ba8Ga16Si(30-x)Gex. Especially for Sr8Ga16Si(30-x)Gex, 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.
Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8521, Japan.
Y
Y
Takasu
T
T
Hasegawa
N
N
Ogita
M
M
Udagawa
M A
MA
Avila
K
K
Suekuni
T
T
Takabatake