Microstructure evolution of nanoprecipitates in half-Heusler TiNiSn alloys

Chai, Yaw Wang; Kimura, Yuichi

doi:10.1016/j.actamat.2013.07.030

Cited by 56 publications

(54 citation statements)

References 27 publications

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“…The implication is that the deviations from stoichiometry are accommodated by fractional occupancy of Ni in the nominally empty sites for hH, or vacancies in the normally filled sites in fH [16,24]. While the finite width homogeneity range for the fH phase has been discussed previously in the literature [25] much less is known about the solubility range for the hH phase, although prior reports of nanoscale precipitation of fH in hH would clearly imply such solubility [7,17,26].…”

Section: (B)mentioning

confidence: 87%

Microstructure Evolution of Biphasic TiNi1+x Sn Thermoelectric Materials

Verma

Douglas

Krämer

et al. 2016

Metall Mater Trans A

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The effects of thermal treatment on the microstructure of bi-phasic materials comprising halfHeusler (hH) and full-Heusler (fH) phases, as well as on their associated thermal conductivity, are discussed. The focus is on a biphasic hH/fH alloy of nominal stoichiometry TiNi 1.2 Sn, synthesized by containerless (magnetic levitation) induction melting. The alloy samples were exposed to various heat treatments to generate microstructures containing second phase precipitates ranging from ~10 nm to a few micrometers. The materials were characterized with regard to morphology, size, shape and orientation relationship of the fH and hH phases, both of which are present as precipitates within larger regions of the counterpart phase. The solidification path of the alloy and its implications for the subsequent microstructure evolution during heat treatment were elucidated, and relationships with the ensuing thermal conductivity were characterized.

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Section: (B)mentioning

confidence: 87%

Microstructure Evolution of Biphasic TiNi1+x Sn Thermoelectric Materials

Verma

Douglas

Krämer

et al. 2016

Metall Mater Trans A

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“…The large power factors (S 2 /ρ) possessed by HHs make them an obvious choice for thermoelectrics research, but high κ values mean that alterations to the structure must be made to reduce κ lat and achieve high zT values. [7][8][9][10][11][12][13] In addition, simultaneously enhanced S and electrical conductivity (σ = 1/ρ) was reported for Zr 0. 3,5,6 The addition of excess Ni has been found to have a significant impact on the thermoelectric properties.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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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 X 1-x X' x Ni 1+y Sn half-Heusler phases. Variable temperature and time dependent neutron powder diffraction for X = Ti and X = Ti 0.5 Hf 0.5 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 Ti 0.5 Zr 0.5 NiSn 1-z Sb z 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) m e .

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“…11 It is also suggested that in nanoparticle form this second phase can additionally lead to "hot-carrier" filtering process, which enhances the Seebeck coefficient. 14 The question of disorder 15,16 and Ni occupancy [17][18][19][20] in the pseudobinary between XNiSn and XNi 2 Sn has been of general interest. The XYZ half-Heusler crystal structure, space group F 43m, can be thought of as an XZ rocksalt sublattice with half of the tetrahedral sites (in terms of coordination with Z) being occupied by Y, forming a YZ zincblende sublattice; in the full-Heusler XY 2 Z, space group Fm 3m, all 8 of these sites within each unit cell are filled.…”

Section: Introductionmentioning

confidence: 99%

Nanoscale structural heterogeneity in Ni-rich half-Heusler TiNiSn

Douglas

Chater

Brown

et al. 2014

Journal of Applied Physics

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The structural implications of excess Ni in the TiNiSn half-Heusler compound are examined through a combination of synchrotron x-ray and neutron scattering studies, in conjunction with first principles density functional theory calculations on supercells. Despite the phase diagram suggesting that TiNiSn is a line compound with no solid solution, for small x in TiNi 1þx Sn there is indeed an appearance-from careful analysis of the scattering-of some solubility, with the excess Ni occupying the interstitial tetrahedral site in the half-Heusler structure. The analysis performed here would point to the excess Ni not being statistically distributed, but rather occurring as coherent nanoclusters. First principles calculations of energetics, carried out using supercells, support a scenario of Ni interstitials clustering, rather than a statistical distribution. V C 2014 AIP Publishing LLC.

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Microstructure evolution of nanoprecipitates in half-Heusler TiNiSn alloys

Cited by 56 publications

References 27 publications

Microstructure Evolution of Biphasic TiNi1+x Sn Thermoelectric Materials

Microstructure Evolution of Biphasic TiNi1+x Sn Thermoelectric Materials

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

Nanoscale structural heterogeneity in Ni-rich half-Heusler TiNiSn

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