Resolving the true band gap of ZrNiSn half-Heusler thermoelectric materials
Abstract
N-type XNiSn (X = Ti, Zr, Hf) half-Heusler (HH) compounds possess excellent thermoelectric properties, which are believed to be attributed to their relatively high mobility. However, p-type XNiSn HH compounds have poor figures of merit, zT, compared to XCoSb compounds. This can be traced to the suppression of the magnitude of the thermopower at high temperatures. E_g = 2eS_(max)T_(max) relates the band gap to the thermopower peak. However, from this formula, one would conclude that the band gap of p-type XNiSn solid solutions is only one-third that of n-type XNiSn, which effectively prevents p-type XNiSn HHs from being useful thermoelectric materials. The study of p-type HH Zr_(1−x)Sc_xNiSn solid solutions show that the large mobility difference between electrons and holes in XNiSn results in a significant correction to the Goldsmid–Sharp formula. This finding explains the difference in the thermopower band gap between n-type and p-type HH. The high electron-to-hole weighted mobility ratio leads to an effective suppression of the bipolar effect in the thermoelectric transport properties which is essential for high zT values in n-type XNiSn (X = Ti, Zr, Hf) HH compounds.
Additional Information
© 2015 The Royal Society of Chemistry. Received 22nd August 2014; Accepted 29th September 2014; First published online 29 Sep 2014. We gratefully acknowledge the German BMBF joint project TEG 2020. G.J.S. would like to acknowledge funding from the Bosch-BERN program and The Materials Project: supported by Department of Energy's Basic Energy Sciences program under Grant no. EDCBEE, DOE Contract DE-AC02-05CH11231 for their funding. The authors would also like to acknowledge the Molecular Materials Research Center (MMRC) at the California Institute of Technology for use of their optical instruments for measurements in this work. Moreover, we would like to thank Chirranjeevi B. Gopal, Julia Krez, and Fivos Drymiotis for helpful discussions.Attached Files
Published - c4mh00142g.pdf
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Additional details
- Eprint ID
- 55041
- Resolver ID
- CaltechAUTHORS:20150220-083509830
- Bundesministerium für Bildung und Forschung (Germany)
- Bosch-BERN
- DE-AC02-05CH11231
- Department of Energy (DOE)
- Created
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2015-02-20Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field