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DESCRIPTION:Veerle Keppens\, University of Tennessee\n\nMotivated by the se
arch for improved thermoelectric materials\, several compounds have attrac
ted attention that combine the high electron mobilities found in crystals
with a low thermal conductivity approaching values typical for glasses. Th
e common structural feature of these “Electron Crystal Phonon Glasses”
(ECPG) is that they contain loosely bound atoms that reside in a large cr
ystalline “cage”. These “rattlers” scatter phonons and greatly red
uce the thermal conductivity of the material. One family of ECPGs is forme
d by the Ge-clathrates Sr 8 Ga 16 Ge 30
sub> and Eu 8 Ga 16 Ge 30 . The pre
sence of the rattler significantly softens the elastic behavior. Combined
with results from low-temperature ultrasonic attenuation\, neutron-scatter
ing\, thermal conductivity and microwave absorption measurements\, it prov
ides clear evidence for the existence of a new type of four-well tunneling
states.\n\n\n\n
DTSTART:20061102T210000Z
LOCATION:Physics Building\, Room 204
SUMMARY:To tunnel or not to tunnel - or why clathrates are so fascinating
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