High Band Degeneracy Contributes to High Thermoelectric Performance in p‐Type Half‐Heusler Compounds

Fu, Chenguang; Zhu, Tiejun; Pei, Yanzhong; Xie, Hanhui; Wang, Heng; Snyder, G. Jeffrey; Liu, Yong; Liu, Yintu; Zhao, Xinbing

doi:10.1002/aenm.201400600

Cited by 288 publications

(211 citation statements)

References 42 publications

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“…[21,35,39,40] [38,39] c) The reported lattice thermal conductivity and calculated κ min of some typical HH materials. [27,37,40,45,49] d) The calculated disorder parameter Γ of (Nb 1−x Ta x ) 0.8 Ti 0.2 FeSb and (V y Nb 1−y ) 0.8 Ti 0.2 FeSb. [8,50] (see details in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…[36] Recently, p-type (V,Nb)FeSb solid solutions were experimentally found to exhibit high TE performance as p-type TE materials because of high band degeneracy in the valence band, and reached an impressive zT of ≈0.8 at 900 K using a high content of Ti as a dopant. [37] Subsequently, an even higher zT of ≈1.1 at 1100 K was achieved in Ti-doped NbFeSb HH compounds via a band engineering approach to reduce the band effective mass. [38] Furthermore, the doping of the more efficient and heavier Hf in NbFeSb achieved an exciting zT of ≈1.47 at 1200 K. [39] This improvement resulted from not only the enhancement of PF (weaker alloy scattering), but also the reduction of κ L (stronger mass fluctuation).…”

Section: Introductionmentioning

confidence: 99%

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Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

Liu

et al. 2017

Advanced Energy Materials

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NbFeSb‐based half‐Heusler alloys have been recently identified as promising high‐temperature thermoelectric materials with a figure of merit zT > 1, but their thermal conductivity is still relatively high. Alloying Ta at the Nb site would be highly desirable because the large mass fluctuation between them could effectively scatter phonons and reduce the lattice thermal conductivity. However, practically it is a great challenge due to the high melting point of refractory Ta. Here, the successful synthesis of Ta‐alloyed (Nb1−xTax)0.8Ti0.2FeSb (x = 0 – 0.4) solid solutions with significantly reduced thermal conductivity by levitation melting is reported. Because of the similar atomic sizes and chemistry of Nb and Ta, the solid solutions exhibit almost unaltered electrical properties. As a result, an overall zT enhancement from 300 to 1200 K is realized in the single‐phase Ta‐alloyed solid solutions, and the compounds with x = 0.36 and 0.4 reach a maximum zT of 1.6 at 1200 K. This work also highlights that the isoelectronic substitution by atoms with similar size and chemical nature but large mass difference should reduce the lattice thermal conductivity but maintain good electrical properties in thermoelectric materials, which can be a guide for optimizing the figure of merit by alloying.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

Liu

et al. 2017

Advanced Energy Materials

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214

160

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“…(2) and shown by both experiments [106][107][108] and theory. 11,31 The study on p-type (V,Nb) FeSb-based materials, a kind of HH alloys with excellent TE performance in the high temperature range (T > 1000 K), 44,109 serves as a good example. 106 DFT calculations show that VFeSb possesses a flatter valence band than that of NbFeSb.…”

Section: Resonant Levelsmentioning

confidence: 99%

Valleytronics in thermoelectric materials

et al. 2018

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The central theme of valleytronics lies in the manipulation of valley degree of freedom for certain materials to fulfill specific application needs. While thermoelectric (TE) materials rely on carriers as working medium to absorb heat and generate power, their performance is intrinsically constrained by the energy valleys to which the carriers reside. Therefore, valleytronics can be extended to the TE field to include strategies for enhancing TE performance by engineering band structures. This review focuses on the recent progress in TE materials from the perspective of valleytronics, which includes three valley parameters (valley degeneracy, valley distortion, and valley anisotropy) and their influencing factors. The underlying physical mechanisms are discussed and related strategies that enable effective tuning of valley structures for better TE performance are presented and highlighted. It is shown that valleytronics could be a powerful tool in searching for promising TE materials, understanding complex mechanisms of carrier transport, and optimizing TE performance.npj Quantum Materials (2018) 3:9 ; doi:10.1038/s41535-018-0083-6 INTRODUCTIONThe demand for renewable energy harvesting has been growing because of the limited fossil fuels and increasing worldwide energy consumption. Thermoelectric (TE) materials, which have the capability of converting heat directly into electricity under a temperature gradient, have been regarded as an alternative option to alleviate energy shortage.1 Though TE devices have already been applied in deep space exploration and solid state cooling, 2,3 the relatively low energy conversion efficiency limits their wide commercialization, 4 which is mainly constrained by the performance of TE materials as characterized by the dimensionless figure of merit, zT = α 2 σT/(κ e + κ L ), where α is the Seebeck coefficient, σ is the electrical conductivity, κ e and κ L are, respectively, the electronic and lattice contributions to the total thermal conductivity κ, and T is the absolute temperature.5 Since all three physical properties (α, σ, and κ) are carrier concentration dependent, zT could reach its maximum value at an optimized carrier concentration. zT max is determined by a combination of intrinsic physical parameters as well as the temperature, all of which integrated into a term called the TE quality factor, B. Higher quality factor B leads to higher zT max at a fixed temperature. With a single parabolic band model in the nondegenerate limit, B could be expressed as:

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“…Meanwhile, effort also exists to optimize alloy composition and search for new ones. 21,25 Despite the materials issues mentioned, HH phase based TE modules were found to have a high device efficiencies reaching 20%. 15,26 From the crystal chemistry viewpoint, antisite disorder seems inevitable.…”

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confidence: 99%

Uncovering high thermoelectric figure of merit in (Hf,Zr)NiSn half-Heusler alloys

Chen

Gao

Zeng

et al. 2015

Applied Physics Letters

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Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn halfHeusler phases (R=Hf, Zr, Ti) are the most studied in view of thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900 o C, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to improved structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys. a)

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High Band Degeneracy Contributes to High Thermoelectric Performance in p‐Type Half‐Heusler Compounds

Cited by 288 publications

References 42 publications

Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

Valleytronics in thermoelectric materials

Uncovering high thermoelectric figure of merit in (Hf,Zr)NiSn half-Heusler alloys

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