Impact of Interstitial Ni on the Thermoelectric Properties of the Half-Heusler TiNiSn
by
Sonia A. Barczak 1, Jim Buckman 2
, Ronald I. Smith 3, Annabelle R. Baker 4, Eric Don 5,6, Ian Forbes 6 and Jan-Willem G. Bos 1,*
Sonia A. Barczak 1, Jim Buckman 2, Ronald I. Smith 3, Annabelle R. Baker 4, Eric Don 5,6, Ian Forbes 6 and Jan-Willem G. Bos 1,*
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.
Materials 2018, 11(4), 536; https://doi.org/10.3390/ma11040536
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)
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.
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Keywords:
half-Heusler; TiNiSn; thermal conductivity; thermoelectric materials
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MDPI and ACS Style
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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