Traversing the Metal-Insulator Transition in a Zintl Phase: Rational Enhancement of Thermoelectric Efficiency in Yb14Mn1−xAlxSb11

Authors


  • This research was funded by NSF DMR-0600742, the Beckman Fellowship program, and NASA/Jet Propulsion Laboratory. CAC acknowledges funding from NSF funded Bridge to Doctorate fellowship. Portions of this work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

Abstract

For high temperature thermoelectric applications, Yb14MnSb11 has a maximum thermoelectric figure of merit (zT) of ∼1.0 at 1273 K. Such a high zT is found despite a carrier concentration that is higher than typical thermoelectric materials. Here, we reduce the carrier concentration with the discovery of a continuous transition between metallic Yb14MnSb11 and semiconducting Yb14AlSb11. Yb14Mn1-xAlxSb11 forms a solid solution where the free carrier concentration gradually changes as expected from the Zintl valence formalism. Throughout this transition the electronic properties are found to obey a rigid band model with a band gap of 0.5 eV and an effective mass of 3 me. As the carrier concentration decreases, an increase in the Seebeck coefficient is observed at the expense of an increased electrical resistivity. At the optimum carrier concentration, a maximum zT of 1.3 at 1223 K is obtained, which is more than twice that of the state-of-the-art Si0.8Ge0.2 flown by NASA.

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