High performance Eu₂ZnSb₂ thermoelectric materials through non-isostructural alloying

The Zintl phase Eu₂ZnSb₂ is a promising thermoelectric material owing to its intrinsically low lattice thermal conductivity. Identifying effective strategies to further optimize its electrical properties and reduce the thermal conductivity is of great significance. In this work, the thermoelectric performance of Eu₂ZnSb₂-based materials has been improved through both isostructural and non-isostructural alloying. Specifically, Eu₂ZnSb₂ was alloyed with Sr₂ZnSb₂, which shares the same 2-1-2 structure, as well as with non-isostructural 9-4 + x-9-type phases, including Ca₉Zn_4.5Sb₉ and Yb₉Zn_4.5Sb₉, which possess similar stoichiometry but distinct crystal frameworks. Alloying Ca/Yb at the Eu site significantly improves the electrical transport properties while simultaneously suppressing the lattice thermal conductivity. Further optimization in carrier concentration is realized through adjusting the concentration of Zn deficiency. As a result, an enhanced peak zT of 1.05 at 723 K and an average zT of up to 0.75 over the temperature range of 300–773 K are achieved in Eu_1.8Yb_0.2Zn_0.99Sb₂.