ISSN:
1013-9826
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Structural characteristics of the high performance cobaltite thermoelectric semiconductorshave been studied intensively by means of X-ray and neutron diffraction measurements and highresolution electron microscopy (HREM). These cobaltites consists of CoO2 triangular conducting sheetsand several different types of block layers, i.e., Na, Ca, Sr single layers, three or four layered rock-saltlayers, where Co-O2 square lattices are situated at their middle, and Bi-O or Tl-O double layers plusalkaline oxygen layers. Cold neutron scattering technique is employed to search possible low-energyexcitation modes, being unique for nearly 1D and 2D crystals, and phonon density of states, DOS, ofseveral high performance cobaltites at temperatures in the range from 10K to the ambient. Low energy,i.e., less than 2meV, excitation modes were found in the three different thermoelectric ceramics, i.e.,γ -Na0.7CoO2, [Ca2CoO3]pCoO2, and [Ca2(Cu,Co)2O4]pCoO2. Possible origin of these low energyexcitations are discussed in terms of low-energy corrugation mode generated due to weak chemicalbondings, for which Van-der-Waals force dominates, between the CoO2 conduction sheets. Thesecharacteristics could be the key to realize low thermal conductivity and high-ZT of these ceramics
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/01/53/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.336-338.826.pdf
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