Low thermal conductivity and promising thermoelectric performance in AxCoSb (A = V, Nb or Ta) half-Heuslers with inherent vacancies

Ferluccio, D. A., Halpin, J. E., MacIntosh, K. L., Quinn, R. J., Don, E., Smith, R. I., MacLaren, D. A. and Bos, J.-W. G. (2019) Low thermal conductivity and promising thermoelectric performance in AxCoSb (A = V, Nb or Ta) half-Heuslers with inherent vacancies. Journal of Materials Chemistry C, 7, pp. 6539-6547. (doi:10.1039/C9TC00743A)

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Abstract

Half-Heuslers with vacancies that are stabilised by a semiconducting electron count offer new opportunities for discovering good thermoelectric performance. Here, we present a comparative study of AxCoSb half-Heuslers (A = V, Nb or Ta) with intrinsic vacancies. Structural analysis demonstrates that each system has a clear preference for a specific vacancy concentration, increasing from 13(1)% (V) to 15(1)% (Nb) and 17(1)% (Ta) with evidence for ~3% V/Co inversion. Hall measurements confirm the decreasing carrier concentration but also signal profound changes to the electronic bandstructure with decreasing density of states effective masses for heavier A elements. V0.87CoSb has an ultralow lattice thermal conductivity, κlat ~ 2.2 W m-1 K-1, which cannot be explained within the Callaway framework. Coupled to a promising power factor, S2/ρ = 2.25 mW m-1 K-2, this results in ZT = 0.6 at 950 K. Nb0.85CoSb has a power factor of S2/ρ = 2.75 mW m-1 K-2 with κ ~ 4.75 W m-1 K-1, yielding a similar ZT = 0.5 at 950 K. Ta0.81CoSb has a microstructure consisting of smaller grains than the other samples, impacting both the carrier and thermal transport, yielding a power factor S2/ρ = 0.75 mW m-1 K-2 and ZT = 0.3 at 950 K. The ultralow κlat for V0.87CoSb may be linked to porosity effects that do not impact on the charge transport, thus affording a new route towards improved performance.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Halpin, Dr John and MacLaren, Dr Donald
Authors: Ferluccio, D. A., Halpin, J. E., MacIntosh, K. L., Quinn, R. J., Don, E., Smith, R. I., MacLaren, D. A., and Bos, J.-W. G.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Journal of Materials Chemistry C
Publisher:Royal Society of Chemistry
ISSN:2050-7526
ISSN (Online):2050-7534
Published Online:13 March 2019
Copyright Holders:Copyright © 2019 Royal Society of Chemistry
First Published:First published in Journal of Materials Chemistry C 7:6539-6547
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
707401Nanostructured half-Heuslers for thermoelectric waste heat recoveryDonald MaclarenEngineering and Physical Sciences Research Council (EPSRC)EP/N017218/1S&E P&A - PHYSICS & ASTRONOMY
722511A Focused Ion Beam Microscopy Facility for Advanced Materials AnalysisIan MaclarenEngineering and Physical Sciences Research Council (EPSRC)EP/P001483/1S&E P&A - PHYSICS & ASTRONOMY