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Materials 2018, 11(4), 536; https://doi.org/10.3390/ma11040536

Impact of Interstitial Ni on the Thermoelectric Properties of the Half-Heusler TiNiSn

1
Institute of Chemical Sciences and Centre for Advanced Energy Storage and Recovery, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
2
Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK
3
ISIS Facility, Rutherford Appleton Laboratory, Harwell Campus, Didcot OX11 0QX, UK
4
Diamond Light Source, Harwell Campus, Didcot OX11 0DE, UK
5
SemiMetrics Ltd., Kings Langley WD4 9WB, UK
6
Department of Physics and Engineering, Northumbria University, Newcastle NE1 8ST, UK
*
Author to whom correspondence should be addressed.
Received: 13 March 2018 / Revised: 27 March 2018 / Accepted: 28 March 2018 / Published: 30 March 2018
(This article belongs to the Special Issue Half-Heusler, Silicide and Zintl-type Thermoelectric Materials)
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Abstract

TiNiSn is an intensively studied half-Heusler alloy that shows great potential for waste heat recovery. Here, we report on the structures and thermoelectric properties of a series of metal-rich TiNi1+ySn compositions prepared via solid-state reactions and hot pressing. A general relation between the amount of interstitial Ni and lattice parameter is determined from neutron powder diffraction. High-resolution synchrotron X-ray powder diffraction reveals the occurrence of strain broadening upon hot pressing, which is attributed to the metastable arrangement of interstitial Ni. Hall measurements confirm that interstitial Ni causes weak n-type doping and a reduction in carrier mobility, which limits the power factor to 2.5–3 mW m−1 K−2 for these samples. The thermal conductivity was modelled within the Callaway approximation and is quantitively linked to the amount of interstitial Ni, resulting in a predicted value of 12.7 W m−1 K−1 at 323 K for stoichiometric TiNiSn. Interstitial Ni leads to a reduction of the thermal band gap and moves the peak ZT = 0.4 to lower temperatures, thus offering the possibility to engineer a broad ZT plateau. This work adds further insight into the impact of small amounts of interstitial Ni on the thermal and electrical transport of TiNiSn. View Full-Text
Keywords: half-Heusler; TiNiSn; thermal conductivity; thermoelectric materials half-Heusler; TiNiSn; thermal conductivity; thermoelectric materials
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Barczak, S.A.; Buckman, J.; Smith, R.I.; Baker, A.R.; Don, E.; Forbes, I.; Bos, J.-W.G. Impact of Interstitial Ni on the Thermoelectric Properties of the Half-Heusler TiNiSn. Materials 2018, 11, 536.

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