Compromise and Synergy in High‐Efficiency Thermoelectric Materials

Given that more than two thirds of all energy is lost, mostly as waste heat, in utilization processes worldwide, thermoelectric materials, which can directly convert waste heat to electricity, provide an alternative option for optimizing energy utilization processes. After the prediction that superlattices may show high thermoelectric performance, various methods based on quantum effects and superlattice theory have been adopted to analyze bulk materials, leading to the rapid development of thermoelectric materials. Bulk materials with two‐dimensional (2D) structures show outstanding properties, and their high performance originates from both their low thermal conductivity and high Seebeck coefficient due to their strong anisotropic features. Here, the advantages of superlattices for enhancing the thermoelectric performance, the transport mechanism in bulk materials with 2D structures, and optimization methods are discussed. The phenomenological transport mechanism in these materials indicates that thermal conductivities are reduced in 2D materials with intrinsically short mean free paths. Recent progress in the transport mechanisms of Bi2Te3‐, SnSe‐, and BiCuSeO‐based systems is summarized. Finally, possible research directions to enhance the thermoelectric performance of bulk materials with 2D structures are briefly considered.

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“…Interested readers are encouraged to refer to other excellent review papers on TE materials. [1,[76][77][78][79] …”

Section: Introductionmentioning

confidence: 99%

Promising Thermoelectric Bulk Materials with 2D Structures

2017

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“…11 Higher symmetry for a crystal in real space results in more equivalent valleys in reciprocal space, and vice versa. 47 etc.…”

Section: Valley Degeneracymentioning

confidence: 99%

“…(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%

“…16 Some excellent reviews focusing on the thermal transport aspects of TE study 17,18 as well as several good comprehensive TE reviews introducing the synergistic design strategies of TE materials have been published in recent years. 1,11,19,20 Nevertheless, there exists a threshold for zT improvement from reducing the thermal conductivity, which is limited to a theoretical minimum (amorphous limit). 21 In contrast there is no theoretical bound to the PF, which leads to the boundless nature of zT.…”

Section: Introductionmentioning

confidence: 99%

“…Recent TE research demonstrates outstanding progress with zT values exceeding the barrier of unity easily and sometimes even above 2, due to inspirations by the low-dimensional design for TE materials 8,9 and the Phonon-Glass-Electron-Crystal concept 10 proposed in 1990s. 11 The rational design strategies for zT enhancement, together with the underlying mechanisms toward high TE performance, can be classified into two categories. One is the reduction of κ L and the other is the increase of TE power factor (PF = α 2 σ).…”

Section: Introductionmentioning

confidence: 99%

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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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Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

Cagnoni

Cojocaru‐Mirédin

et al. 2019

Adv Funct Materials

188

214

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Thermoelectric materials have attracted significant research interest in recent decades due to their promising application potential in interconverting heat and electricity. Unfortunately, the strong coupling between the material parameters that determine thermoelectric efficiency, i.e., the Seebeck coefficient, electrical conductivity, and thermal conductivity, complicates the optimization of thermoelectric energy converters. Main‐group chalcogenides provide a rich playground to alleviate the interdependence of these parameters. Interestingly, only a subgroup of octahedrally coordinated chalcogenides possesses good thermoelectric properties. This subgroup is also characterized by other outstanding characteristics suggestive of an exceptional bonding mechanism, which has been coined metavalent bonding. This conclusion is further supported by a map that separates different bonding mechanisms. In this map, all octahedrally coordinated chalcogenides with good performance as thermoelectrics are located in a well‐defined region, implying that the map can be utilized to identify novel thermoelectrics. To unravel the correlation between chemical bonding mechanism and good thermoelectric properties, the consequences of this unusual bonding mechanism on the band structure are analyzed. It is shown that features such as band degeneracy and band anisotropy are typical for this bonding mechanism, as is the low lattice thermal conductivity. This fundamental understanding, in turn, guides the rational materials design for improved thermoelectric performance by tailoring the chemical bonding mechanism.

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Compromise and Synergy in High‐Efficiency Thermoelectric Materials

Cited by 221 publications

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Promising Thermoelectric Bulk Materials with 2D Structures

Promising Thermoelectric Bulk Materials with 2D Structures

Valleytronics in thermoelectric materials

Chalcogenide Thermoelectrics Empowered by an Unconventional Bonding Mechanism

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