High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys

Populoh, Sascha; Aguirre, Myriam H.; Brunko, Oliver C; Gałązka, K.; Lu, Yuhao; Weidenkaff, Anke

doi:10.1016/j.scriptamat.2012.03.002

Cited by 140 publications

(101 citation statements)

References 18 publications

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“…23 In general, j values are in a range typical for HH compounds with isoelectronic substitution on the X site. 6,8 Tasubstituted compounds show j values comparable to nanostructured Sb-substituted (Zr,Hf)NiSn. 10 Even lower thermal conductivity should be expected when the grain size and shape are refined.…”

Section: à3mentioning

confidence: 99%

“…Each atom site can be substituted for tuning the electron and phonon transport properties. 5 In the scope of the PGEC concept, the most successful strategies for improving the thermoelectric properties of XNiSn HH compounds have been: (1) isoelectric substitution on the X site with Ti and/or Zr and/or Hf to induce point defect scattering in order to suppress j latt ; [6][7][8] (2) Sb doping on the Sn site to adjust the carrier concentration for a high PF; 6,9,10 and (3) nanostructuring to limit the phonon mean free path and further suppress j latt . 11,12 Physical properties of the samples of the same nominal composition show considerable differences, as listed in Table I, raising questions about the influence of different synthesis methods on sample morphology and phase purity.…”

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confidence: 99%

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Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution

Gałązka

Populoh

Xie

et al. 2014

Journal of Applied Physics

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Articles you may be interested inThe thermoelectric performance of Ta substituted (ZrHf)NiSn-based half-Heusler compounds is studied. Here, Ta is used on the Hf site for controlling the charge carrier concentration in contrast to the widely used Sb substitution on the Sn site. The influence of the Ta content on the thermoelectric and transport properties of (Zr 0.3 Hf 0.7-x Ta x )NiSn (x ¼ 0, 0.01, 0.05) is investigated by means of Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall coefficient measurements. The results are analyzed in context of the single parabolic band model. Ta substitution increases the charge carrier concentration and suppresses the influence of impurity band, which is present in the pristine (Zr 0.3 Hf 0.7 )NiSn. Moreover, Ta substitution decouples and simultaneously increases the density-of-states effective mass (m*) and the charge carrier mobility (l), leading to a larger weighted mobility lÁ(m*) 3/2 . The lattice thermal conductivity is slightly suppressed due to increased point defect scattering. As a result, a Figure

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Section: à3mentioning

confidence: 99%

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confidence: 99%

Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution

Gałązka

Populoh

Xie

et al. 2014

Journal of Applied Physics

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“…14, 23 The lattice parameter a of the Zr-Hf-rich phase (HH1) and the Ti-rich phase (HH2) was estimated by a rene-ment of the peak position using LaB 6 as an internal standard and found to be 6.068Å, and 6.001Å, respectively. With increasing Nb content, a decrease in the lattice parameter could be observed.…”

Section: Crystal Structurementioning

confidence: 99%

Optimization of the carrier concentration in phase-separated half-Heusler compounds

et al. 2014

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Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti 0.3Àx Zr 0.35 Hf 0.35 NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor a 2 s and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb.There is evidence in the literature that the average effective mass model is suitable for estimating the optimized carrier concentration of thermoelectric n-type half-Heusler compounds.

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“…Splitting of the Bragg reflection peaks is caused by the coexistence of two 4 HH phases. During the solidification process, the multi-component HH system dissipates into a Ti-poor (HH 1) and a Ti-rich (HH 2) phases [15] . The backscattering electron mode (BSE) SEM images of the n-and p-type samples before and after 500 cycles, shown in Figure 2, revealed the intrinsic phase separation into the main Ti-poor HH 1 phase and the Ti-rich HH 2 phases, which is dendritically interlaced through the microstructure.…”

Section: Resultsmentioning

confidence: 99%

Long-term stability of phase-separated half-Heusler compounds

Krez

Balke

Ouardi

et al. 2015

Phys. Chem. Chem. Phys.

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Half-Heusler (HH) compounds have shown high figure of merits up to 1.5 [1,2,3] . The key to these high thermoelectric efficiencies is an intrinsic phase separation [4] , which occurs in multicomponent Half-heusler compounds and leads to an significantly reduction of the thermal conductivity. For commercial applications, compatible n-and p-type materials are essential and their thermal stability under operating conditions, e.g.for an automotive up to 873 K [5] , needs to be guaranteed. For the first time, the long-term stability of n-and p-type HH materials is proved. We investigated HH materials based on the Ti 0.3 Zr 0.35 Hf 0.35 NiSn-system after 500 cycles (1700 h) from 373 to 873 K. Both compounds exhibit a maximum Seebeck coefficient of | | 210 µV/K and an intrinsic phase separation into two HH phases. The dendritic microstructure is temperature resistant and maintained the low thermal conductivity values ( 4 W/Km). Our results emphasize that phase-separated HH compounds are suitable low cost materials and can lead to enhanced thermoelectric efficiencies beyond the set benchmark for industrial applications.

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High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys

Cited by 140 publications

References 18 publications

Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution

Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution

Optimization of the carrier concentration in phase-separated half-Heusler compounds

Long-term stability of phase-separated half-Heusler compounds

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High figure of merit in (Ti,Zr,Hf)NiSn half-Heusler alloys

Cited by 140 publications

References 18 publications

Improved thermoelectric performance of (Zr0.3Hf0.7)NiSn half-Heusler compounds by Ta substitution

Improved thermoelectric performance of (Zr0.3Hf0.7)NiSn half-Heusler compounds by Ta substitution

Optimization of the carrier concentration in phase-separated half-Heusler compounds

Long-term stability of phase-separated half-Heusler compounds

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Product

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Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution

Improved thermoelectric performance of (Zr_0.3Hf_0.7)NiSn half-Heusler compounds by Ta substitution