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Thermoelectric Materials Frank Bridges, University of California-Santa Cruz, DMR 1005568

Thermoelectric Materials Frank Bridges, University of California-Santa Cruz, DMR 1005568. PbTe:Tl

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Thermoelectric Materials Frank Bridges, University of California-Santa Cruz, DMR 1005568

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  1. Thermoelectric MaterialsFrank Bridges, University of California-Santa Cruz, DMR 1005568 PbTe:Tl When the well known thermoelectric PbTe is doped with up to 2% Tl, the figure of merit, ZT, is dramatically improved; at higher concentrations ZT decreases. The addition of Tl may cause local distortions in the PbTe lattice. The local structure of PbTe:Tl was studied using Extended X-ray Absorption Fine Structure (EXAFS) at the Pb and Tl LIII- and Te K-edge. At 10K the local structure about Pb and Te is well ordered, although disorder of the Pb-Te pair distribution function increases rapidly with increasing T. In contrast the environment around Tl is quite disordered even at 10K within the well ordered host material. This indicates a large variation of the Tl-Te bond lengths presumably as a result of the presence of some Tl(1+). The increased local disorder will result in additional electron scattering which will decrease ZT. Pb LIII-edge r-space data for PbTe with 1%Tl. Notice the strong temperature dependence. Pb Te Rock salt structure of PbTe. Tl LIII-edge r-space data for PbTe:Tl with 1%Tl.

  2. Thermoelectric MaterialsFrank Bridges, University of California-Santa Cruz, DMR 1005568 Graduate and undergraduate students helped collect data at SSRL and were taught EXAFS reduction and analysis techniques. Graduate student Trevor Keiber presented the results on slide 1 at the lattice defect conference (ICDIM) in June. Bridges is a member of the ICDIM International Advisory committee. Undergraduate Brad Car is studying the As-skutterudites for his undergraduate senior thesis project, which will be submitted by the end of Aug 2012. The strong T-dependence shown in the figure indicates that Ce is also a rattler atom in the Arsenides with Einstein temperatures between those for the phosphides and antimonides. In contrast to recent work on NdOs4Sb12, there is no significant (non-thermal) local distortions out to 3-4 neighbors. As-based Skutterudites CeX4As12 Ce Os As Sb and P based skutterudites have been studied extensively but the Asenides have only recently been synthesized. EXAFS studies were carried out for all edges in CeX4As12 (X=Fe, Ru, Os): Ce and Os LIII-edges, and Fe, Ru, and As K-edges. Ce LIII-edge EXAFS

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