Thermoelectric Properties of Selenide Spinels
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THERMOELECTRIC PROPERTIES OF SELENIDE SPINELS G. Jeffrey Snyder*, T. Caillat, and J. -P. Fleurial Jet Propulsion Laboratory/California Institute of Technology 4800, Oak Grove Drive, MS 277-207, Pasadena, CA 91109 *[email protected] ABSTRACT Many compounds with the spinel structure type have been analyzed for their thermoelectric properties. Published data was used to augment experimental results presented here and to select promising thermoelectric spinels. Compounds studied here include Cu0.5Al0.5Cr2Se4, Cu0.5Co0.5Cr2Se4, Cu0.5In0.5Cr2Se4, and CuIr2Se4. Many exhibit low lattice thermal conductivity of about 20 mW/cmK, independent of temperature. Preliminary results are given for two series of compounds that were selected for further study: GaxCu1-xCr2Se4 and ZnxCu1-xCr2Se4. INTRODUCTION The growth of commercial applications of thermoelectric devices depends primarily on increasing the figure of merit, ZT, for thermoelectric materials. The figure of merit is defined as ZT = α2σT/λ, where α is the Seebeck coefficient, σ the electrical conductivity, λ the thermal conductivity, and T is the absolute temperature. Materials with a large α2σ value, or power factor, are usually heavily doped semiconductors, such as Bi2Te3. The thermal conductivity of Figure 1. Illustration of the Spinel unit cell semiconductors is usually dominated by (e.g. ZnCr2Se4) showing Se atoms as phonon or lattice thermal conductivity. spheres Cr atoms (not shown) at the center Thus, one method for finding new, advanced of the shaded octahedra and Zn atoms (not thermoelectric materials is to search for shown) at the center of the shaded semiconductors with low lattice thermal tetrahedra. The cubic unit cell is indicated. conductivity. In this paper we evaluate compounds based on the Spinel structure with general composition A1B2X4 where A and B are transition metals and X is a chalcogen, primarily Se. Previous work on such compounds [1] have shown that a range of metals and insulators exist with this structure type. The structure of Spinel (Figure 1) consists of cubic close packed chalcogen atoms with metal B atoms in half the octahedral holes and metal A atoms in 1/8 of the tetrahedral holes. There can be significant mixing of the different metal atoms on the two metal sites. As suggested by Spitzer [2] the relatively high coordination number of the B atoms in this structure may favor low lattice thermal conductivity. The large cubic unit cells (about 10Å) full of vacant octahedral holes should reduce the lattice thermal conductivity by increasing the scattering of phonons. The multi-valley electronic structure associated with such cubic compounds can be expected to enhance the thermopower.
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G. J. Snyder
Downloaded from https://www.cambridge.org/core. North Carolina State University, on 02 Jan 2018 at 06:46:52, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-626-Z3.3
Mat. Res. Soc. Symp. Vol. 626 © 2000 Materials Research Society
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