Bi2Te3-based Materials Research Articles

Enhancement of Thermoelectric Properties in n-Type Cu0.01Bi2Te2.3+xSe0.7 (0 ≤ x ≤ 0.7) Compounds with Te-Excess

The fine control of antisite defects for Bi2Te3-based materials is necessary to improve their thermoelectric performance using the optimization of a carrier concentration. In this work, we attempted to tune the n-type carrier concentration by forming antisite TeBi defects under a Te-rich condition for Cu0.01Bi2Te2.3+xSe0.7 samples (0 ≤ x ≤ 0.7). The electrical resistivity decreases with increasing the amount of excess Te in the sample of Cu0.01Bi2Te2.3+xSe0.7, which is originated from the increase in the electron carrier concentration for the Te-excess samples. The highest power factor of 2.72 mW/m K2 is obtained at 323 K for Cu0.01Bi2Te2.4Se0.7, which is enhanced by ~ 20% compared to the x = 0 sample. The highest ZT of 0.92 is achieved at 473 K for Cu0.01Bi2Te2.4Se0.7, which is 11% higher than that of x = 0 sample (ZT = 0.83). We demonstrate that the optimization of n-type carrier concentration by forming antisite TeBi defects in n-type Bi2Te3-based materials should be effective for enhancing their thermoelectric performance.

Preparation and Thermoelectric Properties of Graphite/Bi0.5Sb1.5Te3 Composites

Bismuth telluride zone-melting alloys are the most commercially used thermoelectric materials. However, the zone-melting ingots have weak machinability due to the strong preferred orientation. Here, non-textured graphite/Bi0.5Sb1.5Te3 (G/BST) composites were prepared by a powder metallurgy method combined with cold-pressing and annealing treatments. The composition, microstructure, and thermoelectric properties of the G/BST composites with different mass percentages of G were investigated. It was found that G addition could effectively reduce the thermal conductivity and slightly improve the electrical properties of the BST, which resulted in a large enhancement in the figure-of-merit, ZT. The largest ZT for the xG/BST composites with x = 0.05% reached 1.05 at 320 K, which is increased by 35% as compared with that of the G-free BST materials. This work provided an effective method for preparing non-textured Bi2Te3-based TE materials with a simple process, low cost, and large potential in scale production.

Heat transfer enhancement of a modularised thermoelectric power generator for passenger vehicles

Transport represents over a quarter of Europe's greenhouse gas emissions and is the leading cause of air pollution in cities. It has not seen the same gradual decline in emissions as other sectors. Recently, the thermoelectric power generation (TEG) technology emerges as an alternative solution to the emission reduction challenge in this area. In this paper, we present an innovative pathway to an improved heat supply into the concentric shape-adapted TEG modules, integrating the heat pipe technologies. It relies on a phase changing approach which enhances the heat flux through the TEG surface. In order to improve the heat transfer for higher efficiency, in our work, the heat pipes are configured in the radial direction of the exhaust streams. The analysis shows that the power output is adequate for the limited space under the chassis of the passenger car. Much effort can also be applied to obtain enhanced convective heat transfer by adjusting the heat pipes at the dual sides of the concentric TEG modules. Heat enhancement at the hot side of the TEG has an effective impact on the total power out of the TEG modules. However, such improvements can be offset by the adjustment made from the coolant side. Predictably, the whole temperature profile of TEG system is subject to the durability and operational limitations of each component. Furthermore, the results highlight the importance of heat transfer versus the TEG power generation under two possible configurations in the passenger car. The highest power output per repeat unit is achieved at 29.8W per 0.45L with a ZT value 0.87 for a Bi2Te3-based thermoelectric material in our studies. The study provides an insight into a structurally achievable heat exchanger system for other high-temperature thermoelectric materials.

The initial powder-refinement-induced donor-like effect and nonlinear change of thermoelectric performance for Bi2Te3-based polycrystalline bulks

p-type Bi0.5Sb1.5Te3 bulks were prepared from different original sizes of 36–203 μm by the resistance pressing sintering (RPS) method. It was demonstrated that the original powder refinement introduces lattice defects and facilitates a donor-like effect, resulting in a decrease of the carrier concentration and an increase of the effective mass of the carrier. The finer the original powder is, the higher the electrical resistivity and Seebeck coefficient are, and the lower the thermal conductivity is. Although the sintered sample from the smallest sized powders possessed the minimum thermal conductivity, its figure of merit was unsatisfactory due to the low electrical transport performance, and the sintered sample from the 200 ∼ 300 meshed original powders obtained a maximum figure-of-merit of 0.95 at 340 K. In addition, it was observed that the phenomenon of nonlinear change in electrical transport performance with initial powder refinement was due to the percolation effect. In short, the present work confirms that the initial powder size has a great influence on the thermoelectric properties of Bi2Te3-based materials, which should be taken seriously in our follow-up work.

Synthesis and electrical properties of Bi2Te3-based thermoelectric materials doped with Er, Tm, Yb, and Lu

Nanopowders of Bi2Te3 and R0.1Bi1.9Te3 (where R = Er, Tm, Yb, Lu) are obtained by microwave solvothermal synthesis. The powder-like materials are compacted by cold isostatic compression followed by annealing in argon. The influence of the doping agent on the structure and characteristics of the derived materials are investigated. It is demonstrated that the introduction of rare-earth elements (2 at %) into the bismuth-telluride lattice leads to a decrease in the electrical resistivity and to an increase in the Seebeck coefficient. The best thermoelectric properties are obtained for the sample of bismuth telluride doped with thulium.

Thermoelectric properties of I-doped n-type Bi2Te3-based material prepared by hydrothermal and subsequent hot pressing

I-doped Bi2Te3−xIx (x=0, 0.05, 0.1, 0.2) flower-like nanoparticles were synthesized by a hydrothermal method through a careful adjustment of the amount of ethylenediamine tetraacetic acid surfactant. The nanopowders of flower-like nanoparticles were hot-pressed into bulk pellets and the thermoelectric properties of the pellets were investigated. The results showed that I-doping decreased the electrical resistivity effectively, and the thermal conductivitives of the Bi2Te3−xIx bulk samples was lower because of the closer atomic mass of I compared to Te. As a result, a ZT value of 1.1 was attained at 448K for the Bi2Te2.9I0.1 sample.

Graphene Quantum Dots Embedded in Bi2Te3 Nanosheets To Enhance Thermoelectric Performance

Novel Bi2Te3/graphene quantum dots (Bi2Te3/GQDs) hybrid nanosheets with a unique structure that GQDs are homogeneously embedded in the Bi2Te3 nanosheet matrix have been synthesized by a simple solution-based synthesis strategy. A significantly reduced thermal conductivity and enhanced powder factor are observed in the Bi2Te3/GQDs hybrid nanosheets, which is ascribed to the optimized thermoelectric transport properties of the Bi2Te3/GQDs interface. Furthermore, by varying the size of the GQDs, the thermoelectric performance of Bi2Te3/GQDs hybrid nanostructures could be further enhanced, which could be attributed to the optimization of the density and dispersion manner of the GQDs in the Bi2Te3 matrix. A maximum ZT of 0.55 is obtained at 425 K for the Bi2Te3/GQDs-20 nm, which is higher than that of Bi2Te3 without hybrid nanostrucure. This work provides insights for the structural design and synthesis of Bi2Te3-based hybrid thermoelectric materials, which will be important for future development of broadly functional material systems.

High thermoelectric performance of p-BiSbTe compounds prepared by ultra-fast thermally induced reaction

High performance Bi2Te3-based thermoelectric material and modules with a conversion efficiency of 5.2% under a temperature gradient of 250 K were synthesized by TIFS.

Corrosion Behavior of Bi2Te3-Based Thermoelectric Materials Fabricated by Melting Method

Bi2Te3-based compounds are used practically as thermoelectric cooling materials. Bi2Te3–Sb2Te3 or Bi2Te3–Bi2Se3 pseudobinary system compounds are usually applied as p- or n-type material, respectively. Atmospheric water may condense on the surface of thermoelectric materials constituting Peltier modules, depending on their operating environment. Very few studies on the corrosion resistance of Bi2Te3-based compounds have been reported in literature. Moreover, the detailed corrosion behavior of Bi2Te3-based compounds remains unclear. In this study, the corrosion behavior of cleavage planes of Bi2Te3-based compounds fabricated by a melting method has been investigated. Bi2Te3, Sb2Te3, and Bi2Se3 were prepared by the vertical Bridgman method, respectively. Their electrochemical properties evaluated at room temperature by cyclic voltammetry in a standard three-electrode cell with naturally aerated 0.6 mass% or 3.0 mass% NaCl solution as working electrolyte. The c-planes of Bi2Te3 and Sb2Te3 exhibited similar corrosion potential. The corrosion potential of c-plane of Bi2Se3 was more cathodic compared with that of the telluride. The passive current density of the Bi2Te3-based compounds was single or double digit lower than that of stainless steel. X-ray photoelectron spectroscopy results for the electrolyte after testing indicated the possibility that a corrosion product diffuses to the environment including NaCl for Sb2Te3 and Bi2Se3.

Anomalous thermoelectricity in strained Bi2Te3 films.

Bi2Te3-based alloys have been intensively used for thermoelectric coolers and generators due to their high Seebeck coefficient S. So far, efforts to improve the S have been made mostly on changing the structures and components. Herein, we demonstrate an anomalous thermoelectricity in strained Bi2Te3 films, i.e., the value of S is obviously changed after reversing the direction of temperature gradient. Further theoretical and experimental analysis shows that it originates from the coupling of thermoelectric and flexoelectric effects caused by a stress gradient. Our finding provides a new avenue to adjust the S of Bi2Te3-based thermoelectric materials through flexoelectric polarization.

Enhanced thermoelectric performance of Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ∼20% increase in the power factor and an ∼60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

High efficiency Bi2Te3-based materials and devices for thermoelectric power generation between 100 and 300 °C

High efficiency Bi2Te3-based thermoelectric materials and devices with energy conversion efficiencies of up to 6.0% under a temperature gradient of 217 K.

Effects of doping on the positional uniformity of the thermoelectric properties of n-type Bi2Te2.7Se0.3 polycrystalline bulks

The reproducibility problem is one of the central issues in n-type Bi2Te3-based thermoelectric materials. We herein investigate the effects of doping on the positional uniformity of the electronic transport properties of spark-plasma-sintered Bi2Te2.7Se0.3 polycrystalline bulks. Both the electrical conductivity and the Seebeck coefficient showed severe deviations with position in the pristine Bi2Te2.7Se0.3 bulk due to the variation in carrier concentration originating from the formation of Te- and Se-site vacancies. This non-uniformity problem could be significantly improved by the addition of excess elemental Cu and Te. Uniformity enhanced by Cu addition might be considered to be related with the suppression of Te/Se evaporation in the presence of intercalated Cu atoms. A maximum power factor value of ∼2.72 mW/mK2 at 300 K was obtained for Cu0.01Bi2Te2.7Se0.3.

Enhancement of the thermoelectric figure of merit in n-type Cu0.008Bi2Te2.7Se0.3 by using Nb doping

Doping with foreign atom has been shown to be an effective way to enhance the dimensionless figure of merit ZT of Bi2Te3-based thermoelectric raw materials. Herein, we report that doping with Nb is effective in enhancing the Seebeck coefficient of n-type Cu0.008Bi2Te2.7Se0.3 polycrystalline bulks. Considering compensation of the Seebeck coefficient due to decrease of the electrical conductivity in Nb-doped compositions, the absolute value of Seebeck coefficient rather increased benefiting from an enhancement of the density of states (DOS) effective mass m* from 1.09m 0 (Cu0.008Bi2Te2.7Se0.3) to 1.21m 0 − 1.27m 0 (Cu0.008Bi2−x Nb x Te2.7Se0.3) due to a DOS engineering effect. The values of ZT were 0.84 at 300 K and 0.86 at 320 K for Cu0.008Bi1.99Nb0.01Te2.7Se0.3. This compositional tuning approach highlights the possibility of further enhancement of ZT for n-type Bi2Te3-based compounds by using a combination of nanostructuring technologies to reduce the thermal conductivity.

Interfacial Reaction and Shear Strength of SnAgCu/Ni/Bi2Te3-Based TE Materials During Aging

As a diffusion barrier layer, Ni is widely applied in power electronics packaging, especially in thermoelectric devices. This paper presents the variation of Ni diffusion barrier layer during aging and failure mechanisms of thermoelectric device joints. The thermoelectric joint consists of Sn96.5Ag3.0Cu0.5 (SAC305) solder and Bi2Te3-based thermoelectric materials such as Bi0.5Sb1.5Te3 and Bi1.8Sb0.2Se0.15Te2.85 during service. The result shows that with the increasing aging time, Ni layer was constantly consumed by SAC305 and Bi2Te3-based thermoelectric materials simultaneously. The reaction products are (Cu,Ni)6Sn5 and NiTe or Ni(Bi,Te), respectively. Besides, the shear strength of SAC305/Bi0.5Sb1.5Te3 joint or SAC305/Bi1.8Sb0.2Se0.15Te2.85 joint gets gradually decreased and thermoelectric conversion performance gets worse. Meantime, the different failure mechanisms are also compared between SAC305/Bi0.5Sb1.5Te3 couple joints and SAC305/Bi1.8Sb0.2Se0.15Te2.85 couple joints.

Development of Thermoelectric Fibers for Miniature Thermoelectric Devices

Miniature thermoelectric (TE) devices may be used in a variety of applications such as power sources of small sensors, temperature regulation of precision electronics, etc. Reducing the size of TE elements may also enable design of novel devices with unique form factor and higher device efficiency. Current industrial practice of fabricating TE devices usually involves mechanical removal processes that not only lead to material loss but also limit the geometry of the TE elements. In this project, we explored a powder-processing method for the fabrication of TE fibers with large length-to-area ratio, which could be potentially used for miniature TE devices. Powders were milled from Bi2Te3-based bulk materials and then mixed with a thermoplastic resin dissolved in an organic solvent. Through an extrusion process, flexible, continuous fibers with sub-millimeter diameters were formed. The polymer phase was then removed by sintering. Sintered fibers exhibited similar Seebeck coefficients to the bulk materials. However, their electrical resistivity was much higher, which might be related to the residual porosity and grain boundary contamination. Prototype miniature uni-couples fabricated from these fibers showed a linear I–V behavior and could generate millivolt voltages and output power in the nano-watt range. Further development of these TE fibers requires improvement in their electrical conductivities, which needs a better understanding of the causes that lead to the low conductivity in the sintered fibers.

Electronic structures and thermoelectric properties of La or Ce-doped Bi2Te3 alloys from first principles calculations

Thermoelectric properties of La or Ce-doped Bi2Te3 alloys were systematically investigated by ab initio calculations of electronic structures and Boltzmann transport equations. The Seebeck coefficient of p-type LaBi7Te12 and La2Bi6Te12 was larger than that of Bi2Te3, because La doping increased the effective mass of carriers. On the other hand, the electrical conductivity of LaBi7Te12 and La2Bi6Te12 decreased, which caused a reduction of power factor of these La-doped Bi2Te3 alloys in comparison with Bi2Te3. The influence of Ce doping on the band structure and thermoelectric properties of Bi2Te3 was similar to that of La doping. The theoretical calculation provided an insight into the transport properties of La or Ce-doped Bi2Te3-based thermoelectric materials.

Mechanically enhanced p- and n-type Bi2Te3-based thermoelectric materials reprocessed from commercial ingots by ball milling and spark plasma sintering

Abstract Ball milling (BM) combined with spark plasma sintering (SPS) is increasingly used for fabricating high-performance thermoelectric materials. This work was conducted to clarify the effects of BM and SPS on the electrical transport and thermoelectric properties of both p - and n -type Bi 2 Te 3 based materials using commercially available p -type (Bi,Sb) 2 Te 3 and n -type Bi 2 (Se,Te) 3 ingots. Interestingly, it is found that BM and SPS differently affected the electrical properties of p - and n -type Bi 2 Te 3 -based thermoelectric materials; the dimensionless thermoelectric figure of merit ( ZT ) increases in p -type Bi 0.5 Sb 1.5 Te 3 but decreases somewhat in n -type Bi 2 Te 2.7 Se 0.3 after BM and SPS. Hall experiments reveal the reason for this difference. Both p -type and n -type sintered materials show 2–3 times higher mechanical strength than the ingots because of microstructure refinement effect, which has been measured by using a small-sized biaxial bending test. The improved mechanical properties are in favor for device fabrication.

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te₃.

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects.

Bi-Te계 열전소재 연구 동향

Thermoelectric (TE) technology is becoming increasingly important in applications of solid-state cooling and renewable energy sources. Bi₂Te₃-based TE materials are widely used in small-scale cooling and temperature control applications; however, higher levels of TE performance are required for new applications such as large-scale cooling (e.g., domestic refrigerators or air conditioners) and for highly efficient power generation system. Recently, the TE performance of Bi₂Te₃-based materials has been remarkably enhanced by the introduction of nanostructuring technologies which can be used to prepare TE raw materials. Because it takes into account the theoretical and experimental characteristics, nanostructuring has been shown to be one of the most promising ways to realize the simultaneous control of the electronic and thermal transport properties. In this review, emphasis is placed on bulk-type nanostructured Bi₂Te₃-based TE materials. Nanostructuring technologies for enhanced TE performance are summarized, and a few important strategies are presented.