The synthesis and characterization of new compounds is essential for developing new and improved technologies for energy conversion. Thermoelectric devices have the capacity to convert waste heat from other processes to electricity and Zintl phases have been shown to be efficient materials for this application. Performance of thermoelectric devices is governed by a dimensionless figure-of-merit, zT, that scales with conversion efficiency of a particular material. An ideal thermoelectric material with high zT must achieve low electrical resistivity and low thermal conductivity. Since the properties related to zT are inherently coupled, enhancing efficiencies is a difficult task as improvement of one property often works to the detriment of others. The solid solution of the Zintl phase, Yb2-xEuxCdSb2, presents such an optimal structure and here we characterize its thermoelectric properties above room temperature. Yb2-xEuxCdSb2 crystallizes in a polar space group and is similar to Ca2CdSb2 except for a small distortion that removes the center of inversion. The lack of an inversion center, which splits degeneracies compared to the higher symmetry structure, translates into a more complex phonon spectrum and phonon-phonon interaction and thereby lowers the thermal conductivity and increases the figure of merit. Compared to Ca- or Ba-based compounds the noncentrosymmetric space group is unique to this combination of Yb and Eu. The structure and properties of this system will be presented and discussed for thermoelectric applications.

Synthesis and characterization of the Zintl phase Yb2-xEuxCdSb2 for direct thermal to electrical energy conversion

255th National Meeting (2018)

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