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

Daniella A. Ferluccio, John E. Halpin, Kathryn L. Macintosh, Robert J. Quinn, Eric Don, Ronald I. Smith, Donald A. Maclaren, Jan Willem G. Bos

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17 Citations (Scopus)
22 Downloads (Pure)

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.

Original languageEnglish
Pages (from-to)6539-6547
Number of pages9
JournalJournal of Materials Chemistry C
Volume7
Issue number22
DOIs
Publication statusPublished - 13 Mar 2019

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