Enhancement of Power Factor in A Thermoelectric Composite With A Periodic Microstructure
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Enhancement of Power Factor in a Thermoelectric Composite with a Periodic Microstructure
Leonid G. Fel, Yakov M. Strelniker, and David J. Bergman School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 Israel ABSTRACT The thermoelectric power factor has been calculated for a two-constituent composite medium, where one constituent is a “high quality thermoelectric” while the other constituent is a “benign metal”, with large electrical and thermal conductivities but poor thermoelectric properties. It was recently discovered that, in such a mixture, the power factor could be greatly enhanced by an appropriate choice of microstructure. Here we report on a study of three periodic microstructures with cubic point symmetry under rotations: simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC) arrays of identical spheres of the benign metal embedded in the high quality thermoelectric host. We show detailed results for these microstructures in the case where the benign metal constituent is Copper, while the high quality thermoelectric constituent is the thermoelectric alloy (Bi2Te3)0.2 (Sb2Te3)0.8. 1. Recently, it was shown that the thermoelectric power factor of a high quality thermoelectric material can be enhanced by mixing it together with a “benign metal” (i.e., a metal with large electrical and thermal conductivities but a small Seebeck coefficient, and hence with poor thermoelectric properties) in the form of a two-constituent composite medium [1]. This was demonstrated in some very simple microstructures (see Fig. 1). One of those was a parallel slabs sandwich, which is a very anisotropic medium. The other was an isotropic coated spheres assemblage. The last one is a very artificial kind of microstructure, where the system is made up entirely of coated spheres, with a spherical core of the benign metal constituent and a concentric spherical shell of the high quality thermoelectric constituent, and with each sphere having the same core-to-shell volume ratio, even though those spheres must come in many different sizes in order to fill up the entire volume. A realistic microstructure would have to have some disorder in the positions, sizes, and shapes of the constituent grains and possible coatings. As a first step towards a consideration of such realistic microstructures, we have performed detailed calculations on some periodic microstructures. Those are much easier to carry out, using algorithms previously developed for evaluating the bulk effective electrical conductivity of periodic composites [2]. Here we report on studies of three microstructures that exhibit a cubic point symmetry under rotations: simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC) arrays of identical spheres of the benign metal embedded in the high quality thermoelectric host. 2. The thermoelectric power factor W is a material parameter defined by
W ≡ σα 2 ,
where σ is the electrical conductivity at zero temperature gradient while
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