Nonstoichiometry in the Zintl phase Yb1-δZn2Sb2 as a route to thermoelectric optimization

Alex Zevalkink, Wolfgang G. Zeier, Ethan Cheng, Jeffrey Snyder*, Jean Pierre Fleurial, Sabah Bux

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations

Abstract

Classically, Zintl phases are defined as valence-precise line compounds and are thus expected to exhibit intrinsic semiconducting behavior. Contradicting this definition are AZn2Sb2 Zintl compounds ( A = Ca, Sr, Eu, Yb), which exhibit metallic behavior due to high concentrations of cation vacancies, according to recent density functional calculations. Here, we use synchrotron diffraction and high-temperature electronic and thermal transport properties to show that the phase width of Yb1-δZn2Sb2 is wide enough to allow for significant variation and optimization of the thermoelectric properties within the single phase region. Samples with nominal compositions of YbxZn2Sb2 (0.98 < x < 1.05) were synthesized using a solid-state process. With decreasing synthetic Yb content, synchrotron X-ray diffraction reveals decreased lattice parameters, decreased occupancy of the Yb site, and a relaxation of the tetrahedral angles within the Zn2Sb2 sheets. In Yb-deficient samples, the carrier concentration can be controlled by varying x, whereas, in samples with excess Yb, the carrier concentration remains constant and p-type. Fully intrinsic semiconducting behavior was not obtained, suggesting that a slightly Yb-deficient composition is thermodynamically preferable to the valence-precise stoichiometry of δ = 0. Tuning the vacancy concentration provides a new route to controlling the electronic properties in Yb1-δZn2Sb2 and leads to a 50% improvement in the thermoelectric figure of merit (zT = 0.85 at 773 K) compared to previously reported values for unalloyed YbZn2Sb2. (Graph Presented).

Original languageEnglish (US)
Pages (from-to)5710-5717
Number of pages8
JournalChemistry of Materials
Volume26
Issue number19
DOIs
StatePublished - Oct 14 2014

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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