Influence of the Triel Elements (M = Al, Ga, In) on the Transport Properties of Ca_5M_2Sb_6 Zintl Compounds
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.
Additional Information
© 2012 American Chemical Society. Received: February 15, 2012 Revised: May 8, 2012. Publication Date (Web): May 22, 2012. We thank Eric S. Toberer for many helpful discussions. We gratefully acknowledge the Jet Propulsion Laboratory and the National Science Foundation for support, as well as the generous support of Marcella Bonsall for Caltech's Summer Undergraduate Research Program. The authors also acknowledge the Molecular Materials Research Center, part of the Beckman Institute at the California Institute of Technology, for providing equipment for optical absorption measurements. The authors declare no competing financial interest.Additional details
- Eprint ID
- 32367
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- CaltechAUTHORS:20120711-150741811
- JPL
- NSF
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2012-07-12Created from EPrint's datestamp field
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2021-11-09Created from EPrint's last_modified field