Improving the thermoelectric properties of half-Heusler TiNiSn through inclusion of a second full-Heusler phase: Microwave preparation and spark plasma sintering of TiNi1+xSn

Christina S. Birkel, Jason E. Douglas, Bethany R. Lettiere, Gareth Seward, Nisha Verma, Yichi Zhang, Tresa M. Pollock, Ram Seshadri, Galen D. Stucky

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Abstract

Half-Heusler thermoelectrics offer the possibility to choose from a variety of non-toxic and earth-abundant elements. TiNiSn is of particular interest and-with its relatively high electrical conductivity and Seebeck coefficient-allows for optimization of its thermoelectric figure of merit, reaching values of up to 1 in heavily-doped and/or phase-segregated systems. In this contribution, we used an energy- and time-efficient process involving solid-state preparation in a commercial microwave oven and a fast consolidation technique, Spark Plasma Sintering, to prepare a series of Ni-rich TiNi 1+xSn with small deviations from the half-Heusler composition. Spark Plasma Sintering plays an important role in the process by being a part of the synthesis of the material rather than solely a densification technique. Synchrotron powder X-ray diffraction and microprobe data confirm the presence of a secondary TiNi2Sn full-Heusler phase within the half-Heusler matrix. We observe a clear correlation between the amount of full-Heusler phase and the lattice thermal conductivity of the samples, resulting in decreasing total thermal conductivity with increasing TiNi2Sn fraction. This trend shows that phonons are scattered effectively as a result of the microstructure of the materials with full-Heusler inclusions in the size range of microns to tens of microns. The best performing samples with around 5% of TiNi2Sn phase exhibit maximum figures of merit of almost 0.6 between 750 K and 800 K which is an increase of ca. 35% compared to the zT of the parent compound TiNiSn.

Original languageEnglish (US)
Pages (from-to)6990-6997
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume15
Issue number18
DOIs
StatePublished - May 14 2013

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ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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