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X-ray diffraction Rietveld refinements of levitation induction melted, and annealed samples with the nominal (a) TiNiSn composition, x = 0, and (b) two-phase composition with x = 0.15. All peaks could be indexed as Heusler or half-Heusler. Small impurities in (a) are , denoted +, and , denoted *. Note the break in the counts scale in (a).
(a) Optical and (b) scanning electron micrographs of polished sections of the two-phase x = 0.15 sample. In (a), the light regions are the phase, denoted H. In (b), the central region displays a Heusler region that extends between and , and are seen to have half-Heusler precipitates within them, ranging in size from 100 nm to in size.
Electrical and thermal transport measurements of the nominal x = 0 and x = 0.15 samples. (a) Electrical conductivity, (b) Seebeck coefficient (solid line is heating and dashed line is cooling), (c) thermal conductivity, and (d) thermoelectric figure of merit, measured between room temperature and 875 K. (e) The variation of ZT at 800 K as a function of the Ni content, x in .
Schematic of the band energies of the TiNiSn and with respect to a vacuum level. Values correspond to the valence band maximum and conduction band minimum for the semiconductor TiNiSn, and the Fermi level of , the latter positioned in the middle of the band gap of the former.
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