Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics

Barczak, S.A. et al. (2019) Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics. Journal of Materials Chemistry A, 7, 27124. (doi: 10.1039/C9TA10128D)

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We outline a strategy to improve the thermoelectric performance of n-type XNiSn based half-Heusler alloys through Cu doping into vacant tetrahedral sites. A comprehensive combination of structural characterisation and modelling is employed to discriminate the competing mechanisms for thermoelectric enhancement. During synthesis a mineralising effect occurs that improves the homogeneity of the alloying elements Ti, Zr and Hf, and promotes grain growth, leading to a doubling of the electron mobility. In the formed materials, Cu is a strong n-type dopant, like Sb, but occupies the interstitial site and strongly enhances phonon scattering without diminishing carrier mobility (in contrast to interstitial Ni). Simultaneous alloying with Ti, Zr and Hf serves to minimise the thermal conductivity via regular mass disorder and strain effects. A best electronic power factor, S2/ρ, of 3.6 mW m−1 K−2 and maximum ZT of 0.8 at 773 K were observed for a Ti0.5Zr0.25Hf0.25NiCu0.025Sn composition, enabling promising device power densities of ∼6 W cm−2 and ∼8% conversion efficiency from a 450 K gradient. These findings are important because they provide new insight into the mechanisms underpinning high ZT in the XNiSn system and indicate a direction for further improvements in thermoelectric performance.

Item Type:Articles
Glasgow Author(s) Enlighten ID:MacLaren, Dr Donald and Halpin, Dr John
Authors: Barczak, S.A., Quinn, R.J., Halpin, J.E., Domosud, K., Smith, R.I., Baker, A.R., Don, E., Forbes, I., Refson, K., 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 A
Publisher:Royal Society of Chemistry
ISSN (Online):2050-7496
Published Online:19 November 2019
Copyright Holders:Copyright © 2019 The Royal Society of Chemistry
First Published:First published in Journal of Materials Chemistry A 7:27124
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
172181Nanostructured half-Heuslers for thermoelectric waste heat recoveryDonald MaclarenEngineering and Physical Sciences Research Council (EPSRC)EP/N017218/1P&S - Physics & Astronomy
172958A Focused Noble Gas Ion Beam Facility for Materials and Device Nanoanalysis - EQUIPMENT GRANTIan MacLarenEngineering and Physical Sciences Research Council (EPSRC)EP/P001483/1P&S - Physics & Astronomy