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

Thermoelectric properties and phase evolution have been studied in biphasic Ti–Ni–Sn materials containing full-Heusler TiNi{sub 2}Sn embedded within half-Heusler thermoelectric TiNiSn. Materials, prepared by levitation induction melting followed by annealing, were of the nominal starting composition of TiNi{sub 1+x}Sn, 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 TiNi{sub 1.15}Sn. 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.
Authors:
;  [1] ;  [2] ;  [3] ;  [2] ; ;  [1] ;  [3] ;  [4] ;  [1] ;  [2] ;  [2]
  1. Materials Department, University of California, Santa Barbara, California 93106 (United States)
  2. (United States)
  3. Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States)
  4. Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)
Publication Date:
OSTI Identifier:
22275614
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANNEALING; DENSITY FUNCTIONAL METHOD; DIFFERENTIAL THERMAL ANALYSIS; ELECTRON MICROSCOPY; HEUSLER ALLOYS; INTERMETALLIC COMPOUNDS; MELTING; MELTING POINTS; MICROSTRUCTURE; NICKEL; PHASE STABILITY; THERMAL CONDUCTIVITY; THERMOELECTRIC PROPERTIES; TIN; TITANIUM; X-RAY DIFFRACTION