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 similar to 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 Yb14Mn1.05Sb11, 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.