High Temperature Thermoelectric Properties of Yb₁₄MnSb₁₁ Prepared from Reaction of MnSb with the Elements

Compounds of the Yb₁₄MnSb₁₁ structure type are the highest efficiency bulk p-type materials for high temperature thermoelectric applications, with reported figures of merit (ZTs) as high as ∼1.3 at 1275 K. Further optimization of ZT for this structure type is possible with the development of a simple synthetic route. However, this has been difficult to achieve because of the small amount of Mn required compared with Yb and Sb. A simple synthetic route for Yb₁₄MnSb₁₁ has been developed utilizing a combination of ball milling and annealing to produce phase-pure material followed by spark plasma sintering for consolidation. The materials have been characterized by powder X-ray diffraction before and after spark plasma sintering. The stoichiometric reaction of Yb, Sb, and MnSb provides phase-pure powder by X-ray diffraction. Upon cycling to temperatures greater than 1272 K, Yb₁₄MnSb₁₁ shows the presence of Yb₁₁Sb₁₀. Additional samples with 5% and 10% excess Mn were also investigated. Adding 5–10% excess Mn does not change the low temperature properties and improves the high temperature ZT, resulting in a ZT of 1.1–1.2 at 1000 K for Yb₁₄Mn_1.05Sb₁₁, 30–40% improvement over that of the Sn flux reaction. The increase in ZT is attributed to optimization of the carrier concentration. These results provide a reliable method of bulk synthesis of this Zintl phase and open the way for discovery of new compounds with potential for even higher ZT.