Yb₁₁Sb₁₀ and Yb₁₀MnSb₉─Small Change in Structure Leads to Profound Differences in Thermoelectric Properties Investigated Using Zintl Concepts

The Yb–Mn–Sb phase space contains many different Zintl phases of interest for thermoelectric applications. While the Yb11Sb10 phase was first reported and explored years ago, only recently was the Yb10MnSb9 phase first reported. These phases have incredibly similar crystal structures and differ in composition only slightly. Despite these similarities, Yb11Sb10 is reported to be metallic with poor thermoelectric performance, whereas Yb10MnSb9 has been shown to be semiconducting, exhibiting decent thermoelectric properties. In this work, we consider how these phases are both similar and different through an investigation of the crystal structure, electronic band structure, and the experimental transport properties. We then consider how these properties evolve in a two-phase mixture. We show that the thermoelectric properties of samples with intermediate compositions between Yb11Sb10 and Yb10MnSb9 exhibit transport behavior that is well explained by an effective medium theory of a two-phase mixture. This study improves our understanding of the Yb–Mn–Sb phase space, which has major implications for other high-performing thermoelectric materials in the A-M-Sb space (A = Yb, Ca; M = Mn, Mg, Zn, Ga, and In) such as Yb14MnSb11.