Phase stability and property evolution of biphasic Ti-Ni-Sn alloys for use in thermoelectric applications

Jason E. Douglas, Christina S. Birkel, Nisha Verma, Victoria M. Miller, Mao Sheng Miao, Galen D. Stucky, Tresa M. Pollock, Ram Seshadri

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Abstract

Thermoelectric properties and phase evolution have been studied in biphasic Ti-Ni-Sn materials containing full-Heusler TiNi2Sn embedded within half-Heusler thermoelectric TiNiSn. Materials, prepared by levitation induction melting followed by annealing, were of the nominal starting composition of TiNi1+xSn, with x between 0.00 and 0.25. Phases and microstructure were determined using synchrotron X-ray diffraction and optical and electron microscopy. The full-Heusler phase is observed to be semi-coherent with the half-Heusler majority phase. Differential thermal analysis was performed to determine melting temperatures of the end-member compounds. The thermal conductivity is reduced with the introduction of a dispersed, full-Heusler phase within the half-Heusler material. This leads to an increased thermoelectric figure of merit, ZT, from 0.35 for the stoichiometric compound to 0.44 for TiNi1.15Sn. Beyond x = 0.15 ZT decreases due to a rise in thermal conductivity. Density functional theory calculations using hybrid functionals were performed to determine band alignments between the half- and full-Heusler compounds, as well as comparative energies of formation. The hybrid functional band structure of TiNiSn is presented as well.

Original languageEnglish (US)
Article number043720
JournalJournal of Applied Physics
Volume115
Issue number4
DOIs
StatePublished - Jan 28 2014

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Douglas, J. E., Birkel, C. S., Verma, N., Miller, V. M., Miao, M. S., Stucky, G. D., Pollock, T. M., & Seshadri, R. (2014). Phase stability and property evolution of biphasic Ti-Ni-Sn alloys for use in thermoelectric applications. Journal of Applied Physics, 115(4), [043720]. https://doi.org/10.1063/1.4862955