Influence of the triel elements (M = Al, Ga, In) on the transport properties of Ca 5 M 2Sb 6 zintl compounds

Alex Zevalkink*, Gregory S. Pomrehn, Samantha Johnson, Jessica Swallow, Zachary M. Gibbs, G. Jeffrey Snyder

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Scopus citations

Abstract

The Zintl compound Ca 5Al 2Sb 6 has extremely low lattice thermal conductivity (<0.6 W/mK at 1000 K) and tunable electronic properties, making it a promising thermoelectric material for high temperature waste-heat recovery. The current study investigates trends in the chemical and transport properties of the Ca 5M 2Sb 6 compounds (M = Al, Ga, or In), revealing potential routes toward improved thermoelectric properties in this system. Here, we show that isoelectronic M-site substitutions can be used to "fine-tune" the electronic properties of the Ca 5M 2Sb 6 system, without inducing electronic doping effects. Electronic structure calculations reveal that the electronegativity of the M element is a good indicator for the energy level of M electronic states. The effects of M-site substitutions on the effective mass and band gap are reflected in measurements of the high temperature electronic properties of Ca 5M 2Sb 6 samples (M = Al, Ga, and In) which reveal increased hole mobility as well as a smaller thermal band gap in the Ga analogue, relative to Ca 5Al 2Sb 6 and Ca 5In 2Sb 6. Optical absorption measurements reveal a trend in the direct band gaps consistent with both calculations and transport measurements. Additionally, a direct benefit of substituting heavier elements on the Al site arises from the increased density and softer lattice, which leads to reduced sound velocity and lattice thermal conductivity.

Original languageEnglish (US)
Pages (from-to)2091-2098
Number of pages8
JournalChemistry of Materials
Volume24
Issue number11
DOIs
StatePublished - Jun 12 2012

Keywords

  • Zintl phase
  • electronic transport
  • thermal transport
  • thermoelectric

ASJC Scopus subject areas

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

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