Grain by grain compositional variations and interstitial metals – a new route towards achieving high performance in half-Heusler thermoelectrics

Sonia Barczak, John Halpin, Jim Buckman, Rodolphe Decourt, Michaël Pollet, Ronald I. Smith, Donald A. MacLaren, Jan-Willem G. Bos

Research output: Contribution to journalArticle

Abstract

Half-Heusler alloys based on TiNiSn are promising thermoelectric materials characterised by large power factors, good mechanical and thermal stabilities; but they are limited by large thermal conductivities. A variety of strategies have been used to disrupt their thermal transport, including alloying with heavy, generally expensive, elements and nanostructuring, enabling figures of merit, ZT ≥ 1 at elevated temperatures (>773 K). Here, we demonstrate an alternative strategy that is based around the partial segregation of excess Cu leading to grain-by-grain compositional variations, the formation of extruded Cu ‘wetting’ layers between grains and – most importantly – the presence of statistically distributed interstitials that reduce the thermal conductivity effectively through point-defect scattering. Our best TiNiCuySn (y ≤ 0.1) compositions have a temperature-averaged ZTdevice = 0.3-0.4 and estimated leg power outputs of 6-7 W cm-2 in the 323-773 K temperature range. This is a significant development as these materials were prepared using a straightforward processing method, do not contain any toxic, expensive or scarce elements and are therefore promising candidates for large scale production.
LanguageEnglish
Pages4786–4793
Number of pages8
JournalACS Applied Materials and Interfaces
Volume10
Issue number5
Early online date9 Jan 2018
DOIs
Publication statusPublished - 7 Feb 2018

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interstitials
routes
thermal conductivity
metals
thermoelectric materials
figure of merit
point defects
alloying
wetting
temperature
thermal stability
output
scattering

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Barczak, Sonia ; Halpin, John ; Buckman, Jim ; Decourt, Rodolphe ; Pollet, Michaël ; Smith, Ronald I. ; MacLaren, Donald A. ; Bos, Jan-Willem G. / Grain by grain compositional variations and interstitial metals – a new route towards achieving high performance in half-Heusler thermoelectrics. In: ACS Applied Materials and Interfaces. 2018 ; Vol. 10, No. 5. pp. 4786–4793.
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Grain by grain compositional variations and interstitial metals – a new route towards achieving high performance in half-Heusler thermoelectrics. / Barczak, Sonia; Halpin, John; Buckman, Jim; Decourt, Rodolphe; Pollet, Michaël; Smith, Ronald I.; MacLaren, Donald A.; Bos, Jan-Willem G.

In: ACS Applied Materials and Interfaces, Vol. 10, No. 5, 07.02.2018, p. 4786–4793.

Research output: Contribution to journalArticle

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AB - Half-Heusler alloys based on TiNiSn are promising thermoelectric materials characterised by large power factors, good mechanical and thermal stabilities; but they are limited by large thermal conductivities. A variety of strategies have been used to disrupt their thermal transport, including alloying with heavy, generally expensive, elements and nanostructuring, enabling figures of merit, ZT ≥ 1 at elevated temperatures (>773 K). Here, we demonstrate an alternative strategy that is based around the partial segregation of excess Cu leading to grain-by-grain compositional variations, the formation of extruded Cu ‘wetting’ layers between grains and – most importantly – the presence of statistically distributed interstitials that reduce the thermal conductivity effectively through point-defect scattering. Our best TiNiCuySn (y ≤ 0.1) compositions have a temperature-averaged ZTdevice = 0.3-0.4 and estimated leg power outputs of 6-7 W cm-2 in the 323-773 K temperature range. This is a significant development as these materials were prepared using a straightforward processing method, do not contain any toxic, expensive or scarce elements and are therefore promising candidates for large scale production.

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