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Issue 40, 2015
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Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys

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Abstract

Rietveld analysis of neutron powder diffraction data has been used to investigate the compositions of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys prepared by solid state reactions. All samples containing Ti have 2–3% excess Ni, whereas the samples with X = Zr, Hf are almost stoichiometric. Samples with mixed X-metals are characterised by the presence of 3–4 distinct X1−xX′xNi1+ySn half-Heusler phases. Variable temperature and time dependent neutron powder diffraction for X = Ti and X = Ti0.5Hf0.5 demonstrates that both the amount of excess Ni and the phase distribution are stable up to at least 600 °C. Debye temperatures of 367(2) K and 317(2) K were obtained from the thermal displacement parameters. The samples containing Ti are characterised by a ∼0.15 eV bandgap and a monotonously decreasing Seebeck coefficient. The compositions with Zr and Hf have similar bandgap values but show ambipolar transitions. Analysis of the thermoelectric transport data of degenerately doped Ti0.5Zr0.5NiSn1−zSbz samples using a single parabolic band model demonstrates that the transport is limited by alloy scattering and yielded an effective carrier mass of 2.5(1) me.

Graphical abstract: Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys

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Publication details

The article was received on 06 Jul 2015, accepted on 05 Aug 2015 and first published on 05 Aug 2015


Article type: Paper
DOI: 10.1039/C5TC02025E
Citation: J. Mater. Chem. C, 2015,3, 10534-10542
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    Compositions and thermoelectric properties of XNiSn (X = Ti, Zr, Hf) half-Heusler alloys

    R. A. Downie, S. A. Barczak, R. I. Smith and J. W. G. Bos, J. Mater. Chem. C, 2015, 3, 10534
    DOI: 10.1039/C5TC02025E

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