Vacancy site occupation by Co and Ir in half-Heusler ZrNiSn and conversion of the thermoelectric properties from n-type to p-type

Kimura, Yuichi; Tanoguchi, Toshiyasu; Kita, Taizo

doi:10.1016/j.actamat.2010.04.028

Cited by 59 publications

(48 citation statements)

References 23 publications

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“…For example, multiple authors have studied the substitution of Ni by Co and demonstrated that a conversion from n-to p-type behavior for the XNiSn system could be achieved. 22,23 Likewise, Horyn et al 24 studied the effects of substituting Sc for Ti or Zr up to 350 K; the resulting compounds showed promising positive thermopower at room temperature.…”

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confidence: 99%

Resolving the true band gap of ZrNiSn half-Heusler thermoelectric materials

et al. 2015

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N-type XNiSn (X ¼ Ti, Zr, Hf) half-Heusler (HH) compounds possess excellent thermoelectric properties, which are believed to be attributed to their relatively high mobility. However, p-type XNiSn HH compounds have poor figures of merit, zT, compared to XCoSb compounds. This can be traced to the suppression of the magnitude of the thermopower at high temperatures. E g ¼ 2eS max T max relates the band gap to the thermopower peak.However, from this formula, one would conclude that the band gap of p-type XNiSn solid solutions is only one-third that of n-type XNiSn, which effectively prevents p-type XNiSn HHs from being useful thermoelectric materials. The study of p-type HH Zr 1Àx Sc x NiSn solid solutions show that the large mobility difference between electrons and holes in XNiSn results in a significant correction to the Goldsmid-Sharp formula. This finding explains the difference in the thermopower band gap between n-type and p-type HH. The high electron-to-hole weighted mobility ratio leads to an effective suppression of the bipolar effect in the thermoelectric transport properties which is essential for high zT values in n-type XNiSn (X ¼ Ti, Zr, Hf) HH compounds.

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confidence: 99%

Resolving the true band gap of ZrNiSn half-Heusler thermoelectric materials

et al. 2015

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“…For instance, if the difference in thermal expansion between n-and p-type legs would be very large, thermal stress induced during cyclic temperature change should cause severe damage on thermocouples which are comprising the module. Many fairly good p-type half-Heusler compounds have been reported in Sb-base alloy systems, though, not in Sn-base alloy systems [6][7][8][9][10][11]. In addition, they do not have a sufficiently high thermoelectric potential when compared to n-type counterparts.…”

Section: Introductionmentioning

confidence: 94%

“…For designing thermoelectric modules of Sn-base half-Heusler, it is necessary to develop less costly p-type alloys. Thus, one of the authors has proposed the addition of Co and Ir as p-type dopants for the Ni site in n-type ZrNiSn, and has found that Co and Ir atoms preferably occupy the vacancy-site of ZrNiSn while the n-type thermoelectric properties can be converted to p-type [7].…”

Section: Introductionmentioning

confidence: 98%

“…Unit cells of both, half-Heusler type and Heusler type ordered crystal structures, are represented in Figure 1. Many research groups have been working on the application of halfHeusler compounds at high temperatures around 1000 K [1][2][3][4][5][6][7][8][9][10][11]. The most well-known and studied half-Heusler compounds are n-type MNiSn (M = Ti, Zr, Hf), not only because MNiSnbased alloys show potentially high thermoelectric performance but also because these elements are eco-friendly and they eliminate the need for rare or toxic elements.…”

Section: Introductionmentioning

confidence: 99%

“…The most well-known and studied half-Heusler compounds are n-type MNiSn (M = Ti, Zr, Hf), not only because MNiSnbased alloys show potentially high thermoelectric performance but also because these elements are eco-friendly and they eliminate the need for rare or toxic elements. In order to understand the actual thermoelectric properties of half-Heusler compounds, our research group fabricated various nearly single-phase half-Heusler alloys by unidirectional solidification using optical floating zone melting; (Zr x ,Hf 1-x )NiSn (x = 0~1), (Ti,Zr)NiSn 0.04, 0.13, 0.15) and (Ti 0.04 ,Hf 0.96 )NiSn [4][5][6][7]. For example, (Ti 0.15 ,Zr 0.85 )NiSn exhibits a high power factor exceeding 5.0 mW m -1 K -2 while ZT (dimensionless thermoelectric figure of merit) value is about 0.8, and that (Zr 0.5 ,Hf 0.5 )NiSn has a high ZT value of 0.9.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Vacancy-Site Occupation in Half-Heusler Compound ZrNiSn on Phase Stability and Thermoelectric Properties

et al. 2011

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The half-Heusler compound ZrNiSn has a quite small solubility for Ni from the stoichiometric composition towards the Ni-rich direction since Ni atoms are not supposed to occupy the vacancy-site. Nevertheless, Co and Ir atoms preferably occupy the vacancy-site of ZrNiSn, which is contrary to the prediction that they would substitute for Ni sites. This implies that the phase stability of the compound gradually changes toward that of the Heusler compound Zr(Ni,M) 2 Sn (M = Co, Ir). It has been confirmed that there exists a two-phase field between halfHeusler Zr(Ni,Co x )Sn and Heusler Zr(Ni,Co) 2 Sn. The n-type thermoelectric property of ZrNiSn can be converted to p-type by the addition of Co and Ir within the compositional range of the half-Heusler phase. The occupation of vacancy sites by Co and Ir atoms leads to a drastic reduction in the thermal conductivity owing to the enhancement of phonon scattering. With further Co addition, the Heusler phase Zr(Ni,Co) 2 Sn alloys show metallic behavior.

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Enhancing the Thermoelectric Properties via Modulation of Defects in P‐Type MNiSn‐Based (M = Hf, Zr, Ti) Half‐Heusler Materials

Lei

Cichocka

et al. 2023

Adv Funct Materials

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The thermoelectric figure‐of‐merit (zT) of p‐type MNiSn (M = Ti, Zr, or Hf) half‐Heusler compounds is lower than their n‐type counterparts due to the presence of a donor in‐gap state caused by Ni occupying tetrahedral interstitials. While ZrNiSn and TiNiSn, have been extensively studied, HfNiSn remains unexplored. Herein, this study reports an improved thermoelectric property in p‐type HfNi1−xCoxSn. By doping 5 at% Co at the Ni sites, the Seebeck coefficient becomes reaching a peak value exceeding 200 µV K−1 that breaks the record of previous reports. A maximum power factor of ≈2.2 mW m−1 K−2 at 973 K is achieved by optimizing the carrier concentration. The enhanced p‐type transport is ascribed to the reduced content of Ni defects, supported by first principle calculations and diffraction pattern refinement. Concomitantly, Co doping also softens the lattice and scatters phonons, resulting in a minimum lattice thermal conductivity of ≈1.8 W m−1 K−1. This leads to a peak zT of 0.55 at 973 K is realized, surpassing the best performing p‐type MNiSn by 100%. This approach offers a new method to manipulate the intrinsic atomic disorder in half‐Heusler materials, facilitating further optimization of their electronic and thermal properties.

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Vacancy site occupation by Co and Ir in half-Heusler ZrNiSn and conversion of the thermoelectric properties from n-type to p-type

Cited by 59 publications

References 23 publications

Resolving the true band gap of ZrNiSn half-Heusler thermoelectric materials

Resolving the true band gap of ZrNiSn half-Heusler thermoelectric materials

Effect of Vacancy-Site Occupation in Half-Heusler Compound ZrNiSn on Phase Stability and Thermoelectric Properties

Enhancing the Thermoelectric Properties via Modulation of Defects in P‐Type MNiSn‐Based (M = Hf, Zr, Ti) Half‐Heusler Materials

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