Within the realm of rare earth intermetallics, compounds such as Zintl phases and polar intermetallics are known to show promise as suitable thermoelectric materials due to their complexity in their structure, chemical tunability, or high band degeneracy, which can lead to relatively low thermal conductivity and or enhancement of the Seebeck coefficient. A recently reported solid solution of Eu_5.08-xSr_xAl₃Sb₆ is an example of an n-type semimetallic compound electronically situated between a polar intermetallic and a Zintl phase. The structure for the solid solution can be described as a simple pseudo rock salt-like “(Eu/Sr)Sb” structure with one octahedral site in the monoclinic unit cell containing either two orientations of an Al₄ tetrahedron (a dual tetrahedron), or a rare earth or alkali earth metal, or a vacancy in a random fashion. The solid solution, Eu_5-xSr_xAl₃Sb₆, can be prepared by mechanical alloying and heat treatment of the elements. The complexity of the structure contributes to the observed low thermal conductivity and the isovalent substitutions leads to lowering of the thermal conductivity further. Eu_5-xSr_xAl₃Sb₆ shows promising temperature dependent Seebeck coefficients with low electrical resistivity, showing a promising figure of merit, zT. The synthesis, structure, band structure, and thermoelectric properties will be presented.

Luis Garay

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