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Fully Ab-Initio Determination of the Thermoelectric Properties of Half-Heusler NiTiSn: Crucial Role of Interstitial Ni Defects
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Materials 2018, 11(6), 903; https://doi.org/10.3390/ma11060903

Enhancing Thermoelectric Properties through Control of Nickel Interstitials and Phase Separation in Heusler/Half-Heusler TiNi1.1Sn Composites

1
Materials Department, University of California, Santa Barbara, CA 93106, USA
2
Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA
Current address: Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
Current address: Materials Science and Engineering Division, NIST, Gaithersburg, MD 20899, USA.
§
Current address: Intel Corporation, Hillsboro, OR 97124, USA.
*
Author to whom correspondence should be addressed.
Received: 2 May 2018 / Revised: 16 May 2018 / Accepted: 23 May 2018 / Published: 28 May 2018
(This article belongs to the Special Issue Half-Heusler, Silicide and Zintl-type Thermoelectric Materials)
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Abstract

Thermoelectric devices, which allow direct conversion of heat into electrical energy, require materials with improved figures of merit ( z T ) in order to ensure widespread adoption. Several techniques have been proposed to increase the z T of known thermoelectric materials through the reduction of thermal conductivity, including heavy atom substitution, grain size reduction and inclusion of a semicoherent second phase. The goal in these approaches is to reduce thermal conductivity through phonon scattering without modifying the electronic properties. In this work, we demonstrate that Ni interstitials in the half-Heusler thermoelectric TiNiSn can be created and controlled in order to improve physical properties. Ni interstitials in TiNi 1.1 Sn are not thermodynamically stable and, instead, are kinetically trapped using appropriate heat treatments. The Ni interstitials, which act as point defect phonon scattering centers and modify the electronic states near the Fermi level, result in reduced thermal conductivity and enhance the Seebeck coefficient. The best materials tested here, created from controlled heat treatments of TiNi 1.1 Sn samples, display z T = 0.26 at 300 K, the largest value reported for compounds in the Ti–Ni–Sn family. View Full-Text
Keywords: Heusler; TiNiSn; TiNi2Sn; point defect; thermoelectric; phonon scattering Heusler; TiNiSn; TiNi2Sn; point defect; thermoelectric; phonon scattering
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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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Levin, E.E.; Long, F.; Douglas, J.E.; Buffon, M.L.C.; Lamontagne, L.K.; Pollock, T.M.; Seshadri, R. Enhancing Thermoelectric Properties through Control of Nickel Interstitials and Phase Separation in Heusler/Half-Heusler TiNi1.1Sn Composites. Materials 2018, 11, 903.

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