Low Thermal Conductivity and Thermoelectric Performance of Zintl Yb₁₀MnSb₉

The recently discovered Zintl compound Yb₁₀MnSb₉ is a thermoelectric material very close in compositional space to high performing materials such as Yb₁₄MnSb₁₁ and Yb₂₁Mn₄Sb₁₈, making it an interesting candidate for high temperature thermoelectric applications. While others have characterized this material’s crystal structure, here we measure and report electronic and thermal transport data for bulk polycrystalline Yb₁₀MnSb₉ up to 825K. We show that this material has ultralow thermal conductivity, likely due to the previously reported complicated crystal structure with partial occupancies. This ultralow lattice thermal conductivity in conjunction with a higher Seebeck coefficient than in other Yb-Mn-Sb compounds, leads to a moderate zT (thermoelectric figure of merit) of about 0.34 at 825K and is likely to peak at a higher value via material optimization. We approximate a bandgap of about 0.4 eV and expect the zT to be able to reach values as high as 0.33 at 725K given adequate doping (which is comparable to Yb₁₄MnSb₁₁ at that temperature) using a thermoelectric quality factor analysis. Additionally, we suspect that the zT has the potential to reach even higher values by improving the quality factor, B, through grain boundary engineering making it possible to surpass performance of Yb₁₄MnSb₁₁. Here we provide suggestions for future studies to improve thermoelectric performance. We also suggest that other undiscovered 10-1-9 Zintl compounds with thermoelectric potential likely exist, particularly Yb₁₀MgSb₉. This work is the first report of thermal conductivity, approximate bandgap, and zT for this Yb₁₀MnSb₉ compound, and we discuss implications of this material for future thermoelectric study through comparisons to the leading Yb₁₄MnSb₁₁ material.