Yb₁₄MnSb₁₁ as a High- Efficiency Thermoelectric Material

This material could supplant the state-of-theart material, SiGe.

Yb₁₄MnSb₁₁ has been found to be well-suited for use as a p-type thermoelectric material in applications that involve hot-side temperatures in the approximate range of 1,200 to 1,300 K. The figure of merit that characterizes the thermal-to-electric power-conversion efficiency is greater for this material than for SiGe, which, until now, has been regarded as the state-of-the art high-temperature p-type thermoelectric material. Moreover, relative to SiGe, Yb₁₄MnSb₁₁ is better suited to incorporation into a segmented thermoelectric leg that includes the moderate-temperature p-type thermoelectric material CeFe₄Sb₁₂ and possibly other, lower-temperature p-type thermoelectric materials.

Interest in Yb₁₄MnSb₁₁ as a candidate high-temperature thermoelectric material was prompted in part by its unique electronic properties and complex crystalline structure, which place it in a class somewhere between (1) a class of semiconducting valence compounds known in the art as Zintl compounds and (2) the class of intermetallic compounds. From the perspective of chemistry, this classification of Yb₁₄MnSb₁₁ provides a first indication of a potentially rich library of compounds, the thermoelectric properties of which can be easily optimized.

The concepts of the thermoelectric figure of merit and the thermoelectric compatibility factor are discussed in “Compatibility of Segments of Thermo electric Generators” (npo-30798), which appears on page 55. The traditional thermoelectric figure of merit, Z, is defined by the equation

Z = α²/ρκ

where α is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity. Sometimes, in current usage, the term “thermoelectric figure of merit” signifies the product ZT, where T is the absolute temperature. The thermoelectric compatibility factor, s, is defined by the equation

s = [(1 + ZT)^1/2 – 1]/αT.