Investigation of the thermal conductivity of the pentatellurides (Hf 1-X Zr X Te 5 ) using the parallel thermal conducta
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Investigation of the thermal conductivity of the pentatellurides (Hf1-XZrXTe5) using the parallel thermal conductance technique. B. M. Zawilski,1 R. T. Littleton IV,2 Terry M. Tritt,1, 2 D. R. Ketchum3 and J. W. Kolis 3 1 Department of Physics and Astronomy 2 Materials Science and Engineering Department 3 Department of Chemistry Clemson University, Clemson, SC 29634 USA ABSTRACT The pentatelluride materials (Hf1-XZrXTe5) have recently garnered much interest as a potential low temperature thermoelectric material. Their power factor exceeds that of the current Bi2Te3 materials over the temperature range 150 K < T < 350 K. A formidable challenge has been the capability of measuring the thermal conductivity of small needle-like samples (2.0 x 0.05 x 0.1 mm3) such as pentatellurides (HfXZr1-XTe5) due to heat loss and radiation effects. However in order to fully evaluate any material for potential thermoelectric use, the determination of the thermal conductivity of the material is necessary. We have recently developed a new technique called the parallel thermal conductance (PTC) technique to measure the thermal conductivity of such small samples. In this paper we describe the PTC method and measurements of the thermal conductivity of the pentatelluride materials will be presented for the first time. The potential of these materials for low temperature thermoelectric applications will be further evaluated given these results as well as future work and directions will be discussed. INTRODUCTION Recently there have been extensive efforts to develop new thermoelectric (TE) materials 1,2 especially below room temperature. Higher efficiency thermoelectric materials at lower temperatures could eventually lead to TE modules that would be extremely beneficial in 3 localized cooling of many electronic devices. The efficiency of a thermoelectric material is proportional to the dimensionless figure of merit: 2
ZT =
T
2
=
T
,
(1)
where; α is the Seebeck coefficient (or thermoelectric power), σ is the electrical conductivity, ρ (1/σ) is the electrical resistivity, T is the temperature, and λ is the thermal conductivity. The thermopower needs to be sufficiently large so a large Peltier effect is observed. Electrical 2 resistivity should be minimized to reduce the Joule heating (I R) contribution. The thermal conductivity in a good thermoelectric material should also be minimized so that a temperature difference, ∆T, may be established and maintained across the material. The numerator or power factor, α2σT, can typically be tuned through chemical doping and substitution. The total thermal conductivity exhibits contributions from both the lattice and an electronic part (λTOT = λL + λE,
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respectively). The electronic thermal conductivity is related to σ through the Wiedemann-Franz -8 2
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