Changing the Band Gaps by Controlling the Distribution of Initial Particle Size to Improve the Power Factor of N‐Type Bi<sub>2</sub>Te<sub>3</sub> Based Polycrystalline Bulks

Zhang, Chengcheng; Fan, Xi’ an; Hu, Jie; Jiang, Chengpeng; Xiang, Qiusheng; Li, Guangqiang; Li, Yawei; He, Zhu

doi:10.1002/adem.201600696

Cited by 17 publications

(8 citation statements)

References 30 publications

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“…In this work, we found an optimized the HD temperature at 723 K, which balanced the plastic deformation and dynamic recrystallization. As a result, the derived F value is higher than those of n‐type V 2 VI 3 polycrystalline alloys, and is close to that of Bi 2 Te 3 thin film and single crystal (Figure e).…”

Section: Resultssupporting

confidence: 59%

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Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Zhang

et al. 2018

Adv Funct Materials

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Here a progressive hot deformation procedure that endows the benchmark n-type V 2 VI 3 thermoelectric materials with short range disorder (multiple defects), long range order (crystallinity), and strong texture (nearly orientation order) is reported. Not only it is rare for these structural features to coexist but also these structural features elicit the synergistic compositionalmechanical-thermal effects, i.e., a profound interplay among the counts, magnitude, and temperature of hot deformation in relation to the as formed point defects, dislocations, textures, strain clusters, and distortions. Using progressively larger die sets and relatively low hot deformation temperature, rich multiscale microstructures concurrently with a high level of texture comparable to that of zone melted ingot are obtained. The strong donor-like effect significantly increases the majority carrier concentration, suppressing the detrimental bipolar effect. In addition, the multiscale microstructures yield an ultralow lattice thermal conductivity ≈0.31 W m −1 K −1 at 405 K. A record zT ≈ 1.3 at 450 K are attained in progressively hot deformed n-type Bi 1.95 Sb 0.05 Te 2.3 Se 0.7 through the synergistic effects. These results not only promise a better pairing between n-type and p-type legs in device fabrication but also bring our understanding of n-type V 2 VI 3 alloys and hot deformation technique to a new level.device material's figure of merit, zT = σS 2 T/κ, where T, σ, S, and κ are the absolute temperature, the electrical conductivity, the Seebeck coefficient, and the total thermal conductivity (including the lattice component κ ph and the charge carrier component κ el ), respectively. Toward higher zT, defect engineering is invoked to (i) improve the power factor PF = σS 2 through tuning band structure, [2,3] texture, [4,5] and grain boundary; [6,7] and (ii) suppress the κ ph through multiscale microstructures. [8,9] While point defects are of vital importance, [10,11] it is the synergy among various kinds of defects in defect engineering that underlies the high zT.The rhombohedral V 2 VI 3 materials are a hotbed of defect engineering, [12] the success of which make them the benchmark TE materials for solid-state cooling [8,13,14] and low/mid temperature waste heat harvesting. [15][16][17][18][19][20][21][22][23][24] In particular, the high performance of n-type V 2 VI 3 alloys is subject to a delicate balance between strong textures and multiscale microstructures, which is a challenge for materials synthesis and processing. Making the task more challenging, the performance-enhancing mechanisms proved effective in p-type V 2 VI 3 alloys turned out to be less so in n-type V 2 VI 3 alloys. Compared to the p-type counterpart, the n-type V 2 VI 3 material tends to be electrically more anisotropic: the electrical conductivity anisotropy of Thermoelectrics

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Section: Resultssupporting

confidence: 59%

“…d) F values and f) carrier mobility as a function of HD count. e) F values in this work in comparison with those of other n‐type V 2 VI 3 alloys …”

Section: Resultsmentioning

confidence: 73%

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Zhang

et al. 2018

Adv Funct Materials

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“… 6 , 7 However, due to mutual coupling between α, σ, and κ, it is hard to obtain a high zT value. 8 − 11 …”

Section: Introductionmentioning

confidence: 99%

“…With the development of science and technology, growing energy problems seriously threaten the sustainability of human society. Thermoelectric (TE) conversion technology can achieve mutual conversion between heat and electricity without generating pollution, which is applied to temperature difference power generation and solid-state refrigeration. − TE conversion efficiency relies on the dimensionless TE figure of merit expressed as zT = α 2 σ T /κ, where α, σ, T , and κ are Seebeck coefficient, electrical conductivity, absolute temperature, and total thermal conductivity, respectively. − Promising TE materials should have a high α, large σ, and as low as possible κ. , However, due to mutual coupling between α, σ, and κ, it is hard to obtain a high zT value. − …”

Section: Introductionmentioning

confidence: 99%

Optimizing Room-Temperature Thermoelectric Performance of n-Type Bi₂Te_2.7Se_0.3

Wei

et al. 2021

ACS Omega

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Bi 2 Te 3 -based compounds are exclusive commercial thermoelectric materials around room temperature. For n-type compounds, optimal thermoelectric properties are normally obtained at temperatures higher than room temperature to suppress the bipolar effect through increased carrier concentration. We find that doping with trace amounts of Cd and the addition of excess Bi are effective ways to optimize carrier concentration and achieve enhanced room-temperature thermoelectric performance for the Bi 2 Te 2.7 Se 0.3 alloy in this work. For the Cd-doped samples, the replacement of Cd with Bi leads to not only a significant decrease in electron concentration but also apparently reduces the total thermal conductivity. The addition of excess Bi in the samples creates a Bi-rich synthetic atmosphere during the synthesis process, leading to increased Bi Te antisite defects, decreased electron concentration, and reduced total thermal conductivity. Doping a small amount of Cd or adding excess Bi causes optimal thermoelectric performance of the n-type Bi 2 Te 2.7 Se 0.3 sample shifts obviously toward low temperatures, and the samples with 0.4 atom % Cd and 0.8 atom % excess Bi achieve maximum zT of ∼0.97 at 448 K and ∼0.88 at 348 K, respectively.

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“…Compared with zone melting samples, the mechanical properties of SPS sintered samples can be improved by 6–7 times. ,,,− A number of investigations have proven that nanostructuring is undoubtedly successful for p-type Bi 2 Te 3 -based compounds. − However, for n-type Bi 2 Te 3 -based compounds, upon the refinement of grain sizes, the grain boundaries scattering on electrons as well as the weakened orientation of grains in polycrystalline samples lead to a sharp decrease in carrier mobility and significantly degraded electrical transport properties. ,, Besides, the donor-like effect generated in the fracturing process of ingots makes the carrier concentration of the materials increase dramatically, largely deviating from their optimum carrier concentration range. This results in a degradation of the power factor and a significant increase in the total thermal conductivity caused by the sharp rise in electronic thermal conductivity and thus a dramatic deterioration in thermoelectric performance, especially near room temperature. ,− Furthermore, once the donor-like effect is induced, it is very difficult to eliminate the negative effects or to recover through subsequent heat treatment, which, therefore, poses a great challenge to improving the thermoelectric performance of sintered n-type polycrystalline Bi 2 Te 3 -based compounds near room temperature. − …”

Section: Introductionmentioning

confidence: 99%

Removing the Oxygen-Induced Donor-like Effect for High Thermoelectric Performance in n-Type Bi₂Te₃-Based Compounds

Tao

Pan

et al. 2021

ACS Appl. Mater. Interfaces

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Bismuth telluride-based alloys are the best performing thermoelectric materials near room temperature. Grain size refinement and nanostructuring are the core stratagems for improving thermoelectric and mechanical properties. However, the donor-like effect induced by grain size refinement strongly restricts the thermoelectric properties especially in the vicinity of room temperature. In this study, the formation mechanism for the donor-like effect in Bi2Te3-based compounds was revealed by synthesizing five batches of polycrystalline samples. We demonstrate that the donor-like effect in Bi2Te3-based compounds is strongly related to the vacancy defects (V Bi ‴ and V Te ···) induced by the fracturing process and oxygen in air for the first time. The oxygen-induced donor-like effect dramatically increases the carrier concentration from 2.5 × 1019 cm–3 for the zone melting ingot and bulks sintered with powders ground under an inert atmosphere to 7.5 × 1019 cm–3, which is largely beyond the optimum carrier concentration and seriously deteriorates the thermoelectric performance. Moreover, it is found that both avoiding exposure to air and eliminating the thermal vacancy defects (V Bi ‴ and V Te ···) via heat treatment before exposure to air can effectively remove the donor-like effect, producing almost the same carrier concentration and Seebeck coefficient as those of the zone melting ingot for these samples. Therefore, a defect equation of oxygen-induced donor-like effect was proposed and was further explicitly corroborated by positron annihilation measurement. With the removal of donor-like effect and improved texturing via multiple hot deformation (HD) processes, a maximum power factor of 3.5 mW m–1 K–2 and a reproducible maximum ZT value of 1.01 near room temperature are achieved. This newly proposed defect equation of the oxygen-induced donor-like effect will provide a guideline for developing higher-performance V2VI3 polycrystalline materials for near-room-temperature applications.

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Changing the Band Gaps by Controlling the Distribution of Initial Particle Size to Improve the Power Factor of N‐Type Bi₂Te₃ Based Polycrystalline Bulks

Cited by 17 publications

References 30 publications

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Optimizing Room-Temperature Thermoelectric Performance of n-Type Bi₂Te_2.7Se_0.3

Removing the Oxygen-Induced Donor-like Effect for High Thermoelectric Performance in n-Type Bi₂Te₃-Based Compounds

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Changing the Band Gaps by Controlling the Distribution of Initial Particle Size to Improve the Power Factor of N‐Type Bi2Te3 Based Polycrystalline Bulks

Cited by 17 publications

References 30 publications

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V2VI3 Alloys Through Progressive Hot Deformation

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V2VI3 Alloys Through Progressive Hot Deformation

Optimizing Room-Temperature Thermoelectric Performance of n-Type Bi2Te2.7Se0.3

Removing the Oxygen-Induced Donor-like Effect for High Thermoelectric Performance in n-Type Bi2Te3-Based Compounds

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Product

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Changing the Band Gaps by Controlling the Distribution of Initial Particle Size to Improve the Power Factor of N‐Type Bi₂Te₃ Based Polycrystalline Bulks

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Synergistic Compositional–Mechanical–Thermal Effects Leading to a Record High zT in n‐Type V₂VI₃ Alloys Through Progressive Hot Deformation

Optimizing Room-Temperature Thermoelectric Performance of n-Type Bi₂Te_2.7Se_0.3

Removing the Oxygen-Induced Donor-like Effect for High Thermoelectric Performance in n-Type Bi₂Te₃-Based Compounds