Phase stability and property evolution of biphasic Ti–Ni–Sn alloys for use in thermoelectric applications
- Materials Department, University of California, Santa Barbara, California 93106 (United States)
- Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States)
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)
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.
- OSTI ID:
- 22275614
- Journal Information:
- Journal of Applied Physics, Vol. 115, Issue 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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