Critical role of tellurium self-compensation in enhancing the thermoelectric performance of p-Type Bi0.4Sb1.6Te3 alloy

Sun

et al. 2022

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Bi2Te3‐related alloys dominate the commercial thermoelectric market, but the layered crystal structure leads to the dissociation and intrinsic brittle fracture, especially for single crystals that may worsen the practical efficiency. In this work, point defect configuration by S/Te/I defects engineering is engaged to boost thermoelectric and mechanical properties of n‐type Bi2Te3 alloy, which, coupled with p‐type BiSbTe, shows a competitive conversion efficiency for the fabricated module. First, as S alloying suppresses the intrinsic BiTe, antisite defects and forms a donor‐like effect, electronic transport properties are optimized, associated with the decreased thermal conductivity due to the point defect scattering. The periodide compound TeI4 is afterward adopted to further tune carrier concentration for the realization of an optimal ZT. Finally, an advanced average ZT of 1.05 with ultra‐high compressive strength of 230 MPa is achieved for Bi2Te2.9S0.1(TeI4)0.0012. Based on this optimum composition, a fabricated 17‐pair module demonstrates a maximum conversion efficiency of 5.37% under the temperature difference of 250 K, rivaling the current state‐of‐the‐art Bi2Te3 modules. This work reveals the novel mechanism of point defect reconfiguration in synergistic enhancement of thermoelectric and mechanical properties for durably commercial application, which may be applicable to other thermoelectric systems.

Section: Resultsmentioning

confidence: 99%

Mediating Point Defects Endows n‐Type Bi₂Te₃ with High Thermoelectric Performance and Superior Mechanical Robustness for Power Generation Application

Sun

et al. 2022

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“…The stacking faults energy E f is vital for twins’ formation, where low E f means more favorable for the occurrence of twins. Since the sample always keeps in Te‐poor condition even in these samples with δ > 0 (reported in our previous work [ 55 ] ), there are only two cases that should be considered (Figure S4, Supporting Information), 1) stoichiometric Bi 0.4 Sb 1.6 Te 3 and 2) Bi 0.4 Sb 1.6 Te 3 with low Te content. For case two (2), it should be noted that Te vacancy is unstable due to the high formation energy and inclined to be occupied by the Bi or Sb atoms.…”

Section: Resultsmentioning

confidence: 88%

“…However, the twin boundaries might impede the carrier transport. According to data reported in our previous work, [ 55 ] the Bi 0.4 Sb 1.6 Te 3.01 exhibits a similar carrier concentration with the Bi 0.4 Sb 1.6 Te 2.99 (2.37 × 10 19 cm −3 for Bi 0.4 Sb 1.6 Te 3.01 and 2.48 × 10 19 cm −3 for Bi 0.4 Sb 1.6 Te 2.99 ), while the carrier mobility of Bi 0.4 Sb 1.6 Te 3.01 are 36% higher than that of Bi 0.4 Sb 1.6 Te 2.99 (303.1 cm 2 V −1 s −1 for the Bi 0.4 Sb 1.6 Te 3.01 and 222.0 cm 2 V −1 s −1 for the Bi 0.4 Sb 1.6 Te 2.99 ). The only difference between these two samples is that the Bi 0.4 Sb 1.6 Te 2.99 presents much higher twin density than the Bi 0.4 Sb 1.6 Te 3.01 , shown in Figure 2 a,b.…”

Section: Resultsmentioning

confidence: 97%

“…Adding some excess Te ( δ > 0) could modify the carrier transport characteristics and reduce the lattice thermal conductivity to produce an ultra‐high zT value, which has been reported in our previous work. [ 55 ] For the sample with Te content of δ < 0, the electrical conductivity σ in Figure a displays typical semi‐metal features, i.e., decreases with the temperature. Then, by reducing the Te content, sharp σ enhancement is achieved, from 54.7 × 10 3 S m −1 for Bi 0.4 Sb 1.6 Te 3 to 137.5 × 10 3 S m −1 for Bi 0.4 Sb 1.6 Te 2.97 , which mainly results from that decreasing the Te content produces more antisite defects Bi(Sb) Te to generate a large number of holes, verified by the Hall carrier concentration measurement listed in Table S1 (Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

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Nanotwins Strengthening High Thermoelectric Performance Bismuth Antimony Telluride Alloys

Qin

Zhang

et al. 2022

Advanced Science

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Bi2Te3 based thermoelectric alloys have been commercialized in solid‐state refrigeration, but the poor mechanical properties restrict their further application. Nanotwins have been theoretically proven to effectively strengthen these alloys and could be sometimes constructed by strong deformation during synthesis. However, the obscure underlying formation mechanism restricts the feasibility of twin boundary engineering on Bi2Te3 based materials. Herein, thorough microstructure characterizations are employed on a series of Bi0.4Sb1.6Te3+δ alloys to systematically investigate the twins’ formation mechanism. The results show that the twins belong to the annealing type formed in the sintering process, which is sensitive to Te deficiency, rather than the deformation one. The Te deficiency combined with mechanical deformation is prerequisite for constructing dense nanotwins. By reducing the δ below −0.01 and undergoing strong deformation, samples with a high density of nanotwins are obtained and exhibit an ultrahigh compressive strength over 250 MPa, nearly twice as strong as the previous record reported in hierarchical nanostructured (Bi, Sb)2Te3 alloy. Moreover, benefitting from the suppressed intrinsic excitation, the average zT value of this robust material could reach near 1.1 within 30–250 °C. This work opens a new pathway to design high‐performance and mechanically stable Bi2Te3 based alloys for miniature device development.

“…Alongside phase constitution, synthesis methodology and processing temperature play a vital role in determining the physical and transport properties, particularly in (Bi,Sb) 2 Te 3 alloys, which is largely due to their propensity toward nonstoichiometry and tellurium volatility . To further enhance the ZT in p-type Bi 2– x Sb x Te 3 -based materials, which are commercially synthesized using zone melting methods, nanostructuring using ball milling followed by bulk consolidation employing hot pressing has been most successfully demonstrated. ,, However, severe plastic deformation during the milling process was found to induce a “donor-like” effect, which promotes minority charge carriers, that is, electrons, thereby deteriorating the electrical properties. , Alternatively, chemical synthesis − provides a convenient means of obtaining nanocrystals, while spark plasma sintering (SPS) ,,, offers higher heating rates to prevent grain growth and achieve higher densification.…”

Section: Introductionmentioning

confidence: 99%

Compositional Fluctuations Mediated by Excess Tellurium in Bismuth Antimony Telluride Nanocomposites Yield High Thermoelectric Performance

et al. 2021

A high thermoelectric figure of merit (ZT) in state-of-the-art bismuth antimony telluride (BST) composites was attained by an excess telluriumassisted liquid-phase compaction approach. Herein, we report a maximum ZT of ≈ 1.4 at 500 K attained for BST bulk nanocomposites fabricated by spark plasma sintering of colloidally synthesized (Bi,Sb) 2 Te 3 platelets and Te-rich rods. The Terich nanodomains and antimony precipitation during sintering result in compositional fluctuations and atomic ordering within the BST−Te eutectic microstructure, which provides additional phonon scattering and hole contributions. The electrical transport measurement and theoretical calculations corroborate the altered free carrier density via lattice defects and atomic ordering under Te-rich conditions, resulting in a higher power factor. Microstructural studies suggest that reduction in lattice thermal conductivity is due to composite interfaces and defects in the closely packed (Bi,Sb) 2 Te 3 matrix with unevenly distributed Sband Te-rich nanodomains. This work provides an unconventional chemical synthesis route with large scalability for developing high-performance chalcogenide-based bulk nanocomposites for thermoelectric applications.