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Maximum Entropy Method Charge Density Distributions of Novel Thermoelectric Clathrates

Published online by Cambridge University Press:  10 February 2011

B. Iversen ,
A. Bentien ,
A. Palmqvist ,
D. Bryan ,
S. Latturner ,
G.D. Stucky ,
N. Blake ,
H. Metiu ,
G. S. Nolas  and
D. Cox
B. Iversen
Affiliation:
Dept. of Chemistry, University of Aarhus, Århus, Denmark
A. Bentien
Affiliation:
Dept. of Chemistry, University of Aarhus, Århus, Denmark
A. Palmqvist
Affiliation:
Dept. of Applied Surface Chemistry, Chalmers University of Technology, Göteborg, Sweden
D. Bryan
Affiliation:
Dept. of Chemistry, University of California, Santa Barbara, CA, USA
S. Latturner
Affiliation:
Dept. of Chemistry, University of California, Santa Barbara, CA, USA
G.D. Stucky
Affiliation:
Dept. of Chemistry, University of California, Santa Barbara, CA, USA
N. Blake
Affiliation:
Dept. of Chemistry, University of California, Santa Barbara, CA, USA
H. Metiu
Affiliation:
Dept. of Chemistry, University of California, Santa Barbara, CA, USA
G. S. Nolas
Affiliation:
R&D Division, Marlow Industries Inc, Dallas, Texas, USA
D. Cox
Affiliation:
NSLS, Brookhaven National Laboratory, Upton, NY, USA
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Abstract

Recently materials with promising thermoelectric properties were discovered among the clathrates. Transport data has indicated that these materials have some of the characteristics of a good thermoelectric, namely a low thermal conductivity and a high electrical conductivity. Based on synchrotron powder and conventional single crystal x-ray diffraction data we have determined the charge density distribution in Sr8Ga16Ge3O using the Maximum Entropy Method. The MEM density shows clear evidence of guest atom rattling, and this contributes to the reduction of the thermal conductivity. Analysis of the charge distribution reveals that Sr8Ga16Ge30 contains mixed valence alkaline earth guest atoms. The Sr atoms in the small cavities are, as expected, doubly positively charged, whereas the Sr atoms in the large cavities appear negatively charged. The MEM density furthermore suggests that the Ga and Ge atoms may not be randomly disordered on the framework sites as found in the conventional leastsquares refinements.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 590: Symposium R – Applications of Synchrotron Radiation Techniques…V , 1999 , 145
Copyright
Copyright © Materials Research Society 2000

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References

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