Grain-by-Grain Compositional Variations and Interstitial Metals -: A New Route toward Achieving High Performance in Half-Heusler Thermoelectrics

Sonia A. Barczak, John E. Halpin, Jim Buckman, Rodolphe Decourt, Michael Pollet, Ronald I. Smith, Donald A. Maclaren, Jan Willem G. Bos

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)
18 Downloads (Pure)

Abstract

Half-Heusler alloys based on TiNiSn are promising thermoelectric materials characterized by large power factors and 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.

Original languageEnglish
Pages (from-to)4786-4793
Number of pages8
JournalACS Applied Materials and Interfaces
Volume10
Issue number5
Early online date25 Jan 2018
DOIs
Publication statusPublished - 7 Feb 2018

Keywords

  • half-Heusler
  • phase segregation
  • structure-property relationships
  • thermoelectrics
  • TiNiSn

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