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Issue 22, 2019
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Low thermal conductivity and promising thermoelectric performance in AxCoSb (A = V, Nb or Ta) half-Heuslers with inherent vacancies

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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 reveals an increasing vacancy concentration from V (13%) to Nb (15%) to Ta (19%) with evidence for ∼3% V/Co inversion. This decrease in ability to n-type dope these materials is caused by an increase in conduction band dispersion, evident from a decreasing density of states mass from Hall data, leading to a higher cost of populating these antibonding states. 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 strongly impact on the charge transport, thus affording a new route towards improved performance.

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

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Publication details

The article was received on 08 Feb 2019, accepted on 08 Mar 2019 and first published on 13 Mar 2019


Article type: Paper
DOI: 10.1039/C9TC00743A
J. Mater. Chem. C, 2019,7, 6539-6547
  • Open access: Creative Commons BY license
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    Low thermal conductivity and promising thermoelectric performance in AxCoSb (A = V, Nb or Ta) half-Heuslers with inherent vacancies

    D. A. Ferluccio, J. E. Halpin, K. L. MacIntosh, R. J. Quinn, E. Don, R. I. Smith, D. A. MacLaren and J. G. Bos, J. Mater. Chem. C, 2019, 7, 6539
    DOI: 10.1039/C9TC00743A

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