Compatibility factor of segmented thermoelectric generators based on quasicrystalline alloys

Abstract

In this work we present a prospective study on the possible use of certain quasicrystalline alloys in order to improve the efficiency of segmented thermoelectric generators. To this end, we obtain a closed analytical expression for their compatibility factor [G. J. Snyder and T. S. Ursell, Phys. Rev. Lett. 91, 148301 (2003)]. By comparing our analytical results with available experimental data we conclude that a promising high temperature material, compatible with benchmark thermoelectric materials, can be found among AlPdMn based icosahedral quasicrystals. The efficiency of a thermoelectric device depends on the transport properties of the constituent materials and the temperature difference between the hot and cold sides, which sets its Carnot upper limit. Evaluation of new materials for thermoelectric applications is usually made in terms of the dimensionless figure of merit,where T is the temperature, ͑T͒ is the electrical conductivity, ␣͑T͒ is the Seebeck coefficient, e ͑T͒ is the charge carrier contribution to the thermal conductivity, and ph ͑T͒ is the lattice contribution to the thermal conductivity. When considering segmented devices one should also consider the compatibility factor defined by 1since materials with dissimilar s vales cannot be efficiently combined in that case. The thermoelectric compatibility of several materials of current technological interest has been recently reviewed, concluding that a semimetallic material with high p-type thermopower is required for development of segmented generators. 2 In the last few years it has been progressively realized that quasicrystals (QCs) deserve some attention as potential thermoelectric materials (TEMs), since they naturally fulfill the Slack's requirements for a material belonging to the "electronic crystal/phonon glass" class. 3-7 Quite interestingly, relatively high, positive thermopower values ͑+100 − 120 V K −1 ͒ have been reported for representatives of the icosahedral AlPdMn and AlPdRe families in the temperature range 300-600 K. [8][9][10] The main aim of this paper is to show that, by a judicious choice of sample's stoichiometry, 11 suitable candidates for a high temperature material, compatible with PbTe, ͑AgSbTe 2 ͒ 0.15 ͑GeTe͒ 0.85 (TAGS) or skutterudites, may be found among the AlPd͑Re, Mn͒ quasicrystalline alloys.To this end, let us start by briefly summarizing some relevant experimental data. In Tables I and II we list the figure of merit and compatibility factors of different QCs as reported in the literature. At room temperature we observe that the largest s values are comparable to those observed in usual TEMs, like Bi 2 Te 3 or SiGe ͑s Ӎ 1 V −1 ͒. 2 At higher temperatures the most promising QC is i-AlPdMn, which exhibits an s factor larger than those reported for SiGe ͑s Ӎ 1 V −1 ͒ and PbTe ͑s Ӎ 1.2 V −1 ͒, and approaches that of TAGS ͑s Ӎ 2.7 V −1 ͒ at T = 550 K. 2 On the other hand, the s factor corresponding to AlPdRe samples is larger at room temperature (where it exhibits a lower ZT value) than it is at higher temperatures...

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Significantly enhanced thermoelectric figure of merit of p-type Mg3Sb2-based Zintl phase compounds via nanostructuring and employing high energy mechanical milling coupled with spark plasma sintering

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