The effects of YbSb and YbMnSb secondary phases on the high performing thermoelectric material YbMnSb

The Yb 11 Sb 10 Zintl phase has long been reported to be a negative secondary phase in the high performing Yb 14 MSb 11 (M = Mn, Mg, Zn) (14-1-11) thermoelectric material. However there have been discrepancies in the literature regarding the effect of this Yb 11 Sb 10 phase on the thermoelectric performance of 14-1-11 compounds. The recent discovery of Yb 10 MnSb 9 is used here to explain these inconsistencies. Yb 11 Sb 10 and Yb 10 MnSb 9 are very close materials stoichiometrically and crystallographically. However, despite these similarities, these materials exhibit very different transport properties and thus should have differing impacts on the overall thermoelectric performance of 14-1-11. In this work, we consider how these two phases affect the thermoelectric performance of Yb 14 MnSb 11 when present as secondary phases both through an experimental investigation and an effective medium theory model. Secondary phases in thermoelectrics are often regarded as a consistently negative effect and yet here we show that while the presence of Yb 11 Sb 10 in Yb 14 MnSb 11 reduces the thermoelectric performance, the presence of Yb 10 MnSb 9 , even in large amounts does not dramatically reduce the thermoelectric performance and is shown here to even improve performance. This work provides a deeper understanding of previous works regarding 14-1-11 materials and Yb-Mn-Sb phases and paves the way towards practical application. The first exploration of the impact of Yb 11 Sb 10 and Yb 10 MnSb 9 secondary phases in Yb 14 MnSb 11 , explaining years of confusing thermoelectric data.