Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase

Douglas, Jason E.; Birkel, Christina S.; Miao, Mao; Torbet, Chris; Stucky, Galen D.; Pollock, Tresa M.; Seshadri, Ram

doi:10.1063/1.4765358

Cited by 67 publications

(57 citation statements)

References 23 publications

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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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Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…Half-Heuslers, such as TiNiSn, can be alloyed with site defects and semi-coherent full-Heusler secondary phase inclusions. 19 Other promising materials feature superlattices, secondary phase inclusions, and large number of atoms. Magn eli phases with crystallographic shear, such as WO 3Àx , 20 show promising preliminary results, though our fractional kappa plots reveal the Seebeck coefficient will need to be improved to achieve zT > 0.5.…”

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How much improvement in thermoelectric performance can come from reducing thermal conductivity?

Gaultois

Sparks

2014

Applied Physics Letters

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Large improvements in the performance of thermoelectric materials have come from designing materials with reduced thermal conductivity. Yet as the thermal conductivity of some materials now approaches their amorphous limit, it is unclear if microstructure engineering can further improve thermoelectric performance in these cases. In this contribution, we use large data sets to examine 300 compositions in 11 families of thermoelectric materials and present a type of plot that quickly reveals the maximum possible zT that can be achieved by reducing the thermal conductivity. This plot allows researchers to quickly distinguish materials where the thermal conductivity has been optimized from those where improvement can be made. Moreover, through these large data sets we examine structure-property relationships to identify methods that decrease thermal conductivity and improve thermoelectric performance. We validate, with the data, that increasing (i) the volume of a unit cell and/or (ii) the number of atoms in the unit cell decreases the thermal conductivity of many classes of materials, without changing the electrical resistivity.

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“…To investigate this trend, and to explain why a solid solution forms in this Heusler/half-Heusler system (as opposed to, for example, TiNi 1+x Sn, 42 which phase separates), density functional theory calculations were performed. The results of calculating the energy of all of the possible orderings of the Ni vacancies on the two Ni fcc sublattices in a 1×1×1 conventional cell (12-16 atoms) are shown as filled circles in Figure 4(b).…”

Section: Structural Characterizationmentioning

confidence: 99%

Tuning the magnetocaloric response in half-Heusler/Heusler MnNi1+xSb solid solutions

Levin

Bocarsly

Wyckoff

et al. 2017

Phys. Rev. Materials

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Materials with a large magnetocaloric response are associated with a temperature change upon the application of a magnetic field, and are of interest for applications in magnetic refrigeration and thermomagnetic power generation. The usual metric of this response is the gravimetric isothermal entropy change ∆SM . The use of a simple proxy for the ∆SM that is based on density functional theory (DFT) calculations of the magnetic electronic structure, suggests that half-Heusler MnNiSb should be a better magnetocaloric than the corresponding Heusler compound MnNi2Sb. Guided by this observation, we present a study of MnNi1+xSb (x = 0, 0.25, 0.5, 0.75, 1.0) to evaluate relevant structural and magnetic properties. DFT stability calculations suggest that the addition of Ni takes place at a symmetrically distinct Ni site in the half-Heusler structure, and support the observation using synchrotron X-ray diffraction of a homogeneous solid solution between the half-Heusler and Heusler endmembers. There is a maximum in the saturation magnetization at x = 0.5, and the Curie temperature systematically decreases with increasing x. ∆SM for a maximum magnetic field change of ∆H = 5 T monotonically decreases in magnitude from −2.93 J kg −1 K −1 in the half-Heusler to −1.35 J kg −1 K −1 in the Heusler compound. The concurrent broadening of the magnetic transition results in a maximum in the refrigerant capacity at x = 0.75. The Curie temperature of this system is highly tunable between 350 K and 750 K, making it ideal for low grade waste heat recovery via thermomagnetic power generation. The increase in ∆SM with decreasing x may be extendable to other MnNi2Z Heusler systems that are currently under investigation for use in magnetocaloric refrigeration applications.

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Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase

Cited by 67 publications

References 23 publications

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

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

How much improvement in thermoelectric performance can come from reducing thermal conductivity?

Tuning the magnetocaloric response in half-Heusler/Heusler MnNi1+xSb solid solutions

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