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The Dynamics of the Guests in Filled Germanium Clathrates

Published online by Cambridge University Press:  01 February 2011

Raphael P. Hermann ,
Fernande Grandjean ,
Veerle Keppens ,
Werner Schweika ,
George S. Nolas ,
David G. Mandrus ,
Brian C. Sales ,
Hans M. Christen ,
Pierre Bonville  and
Gary J. Long
Raphael P. Hermann
Affiliation:
R.Hermann@ulg.ac.be, University of Liege, Physics, Allee du 6 Aout, 17 Bat. B5, Liege, N/A, 4000, Belgium, ++ 32 4 3663630, ++ 32 4 3664516
Fernande Grandjean
Affiliation:
fgrandjean@ulg.ac.be
Veerle Keppens
Affiliation:
vkeppens@utk.edu
Werner Schweika
Affiliation:
w.schweika@fz-juelich.de
George S. Nolas
Affiliation:
gnolas@cas.usf.edu
David G. Mandrus
Affiliation:
mandrusdg@ornl.gov
Brian C. Sales
Affiliation:
salesbc@ornl.gov
Hans M. Christen
Affiliation:
christenhm@ornl.gov
Pierre Bonville
Affiliation:
bonville@drecam.saclay.cea.fr
Gary J. Long
Affiliation:
glong@umr.edu
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Abstract

In the filled gallium-germanium clathrates, R8Ga16Ge30, where R is Ba, Sr, or Eu, the guests are located in two large cages and are weakly bound to the crystalline clathrate framework. The caged guests exhibit a localized “rattling” vibrational mode that provides an efficient mechanism for reducing the thermal conductivity. Inelastic neutron scattering and nuclear inelastic scattering measurements have yielded the phonon density of states in R8Ga16Ge30; the line width of the localized vibrational modes is found to be an important parameter in determining the lattice thermal conductivity. Neutron diffraction studies on R8Ga16Ge30 have shown that the guests in the larger cage are located off-center, and it was proposed that their jumping about the four off-center locations is responsible for the observed glass-like thermal conductivity at temperatures below 10 K. The detection of such slow guest motion is challenging because the typical time and energy scales involved are ca. 4 ns and 1 µeV, respectively. We have studied the slow europium tunneling dynamics in Eu4Sr4Ga16Ge30 by both Mössbauer and microwave absorption spectroscopy.

Keywords

neutron scatteringMössbauer effectthermal conductivity
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 886: Symposium F – Materials and Technologies fore Direct Thermal-to-Electric Energy Conversion , 2005 , 0886-F10-01
Copyright
Copyright © Materials Research Society 2006

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References

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