Exploration of The Effects of Yb₁₁Sb₁₀ and Yb₁₀MnSb₉ Secondary Phases on The High Performing Zintl Thermoelectric Material Yb₁₄MnSb₁₁

The high performing Zintl thermoelectric material Yb₁₄MnSb₁₁ has been of interest to the thermoelectrics community for years. However, a major challenge with this material is that it exists in a very busy region of phase space, making it susceptible to having considerable amounts of secondary phases. In particular, the Yb₁₁Sb₁₀ phase has been repeatedly reported as a negative secondary phase, but there have been discrepancies in the literature regarding the effect of this phase as a secondary phase in 14-1-11. Since the Yb₁₁Sb₁₀ material is a poor metal, it would be expected to hinder thermoelectric performance, and yet there have been studies where large amounts of this metallic phase have relatively no effect on transport, and even one case where it seemed like the Yb₁₁Sb₁₀ phase contributed to an improvement in the thermoelectric performance. Recently, a related phase, Yb₁₀MnSb₉ has been reported and has been shown to have a high Seebeck coefficient and ultralow thermal conductivity making it a decent p-type thermoelectric material. Despite having very different properties, Yb₁₁Sb₁₀ and Yb₁₀MnSb₉ have extensive crystallographic and stoichiometric similarities, which makes distinguishing between these two phases difficult, especially if they are only present in small amounts as a secondary phases. In this work, we consider the properties of these two possible secondary phases and explore the consequences of these materials as secondary phases in the high performing Yb₁₄MnSb₁₁ material.