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The thermal transport and thermoelectric properties of CsCdX3 (X = Cl, Br) were investigated using first-principles calculations and machine learning interatomic potentials. The lattice thermal conductivity was obtained including the effect of temperature on the phonon dispersion spectrum and the contribution of the diffuson-like phonons, based on the self-consistent phonon (SCP) and two-channel phonon transport theories. We found that diffuson-like phonons contribute significantly to the lattice thermal transport. The ultralow lattice thermal conductivities of CsCdCl3 and CsCdBr3 at 300 K are 0.95 W/mK and 0.57 W/mK, respectively. The large Seebeck coefficient of CsCdCl3 and CsCdBr3 is about 800 μV/K and 700 μV/K at 900 K, due to the multi-valley energy band structure. The calculated maximum ZT of p-type CsCdBr3 is 1.16 at 900 K, larger than most of the reported halide perovskite materials. We suggest that CsCdBr3 is a promising candidate for thermoelectric halide perovskite materials. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is emerging as a promising n-type thermoelectric material (TE) for power harvesting due to its high melting point and large Seebeck coefficient. However, the TE performance of ZnO is limited by high thermal conductivity and low carrier mobility. Adding or doping a divalent element such as cadmium oxide (CdO) can lower the thermal conductivity and enhance the carrier concentration of ZnO. In this paper, the thermoelectric transport properties of ZnO-CdO nanocrystalline thin films are investigated by varying the Zn/Cd ratio at temperatures ranging from room temperature (RT) to 423 K. The electrical conductivity, carrier concentration and mobility of ZnO were enhanced by increasing the Cd concentration. The maximum power factor of 2.75 × 10−4 W m−1 K−2 was obtained at 423 K for the Zn/Cd = 1:3 sample. The thermal conductivity was dominated by lattice thermal conductivity in which Umklapp scattering occurs between anharmonic phonons. The thermal conductivity of ZnO decreased significantly with increasing Cd concentration. The highest estimated figure of merit (ZT) of 0.59 was found at 413 K for the Zn/Cd = 1:3 sample, which is 223 times greater than for ZnO, indicating that the film is efficient in energy generation. [ABSTRACT FROM AUTHOR]

Bismuth telluride-based thermoelectric devices are the only thermoelectric devices that are currently used in large-scale commercial applications. In actual production, nitric acid roughening solution corrodes them and generates a black substance on the surface that is difficult to remove. The exact composition of the black film is not known, which makes its removal even more difficult. In this study, it was observed by x-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) that the black substance may be formed by the reaction of Sb2Te3 in p-type bismuth telluride with nitric acid. Valence analysis by x-ray photoelectron spectrometry (XPS) showed the presence of Te in the black substance in the valence states of Te4+ and Te6+, and Sb in the valence state of Sb3+. Fourier transform infrared spectrometry (FTIR) results showed the existence of four chemical bonds, including νTe-O, νSb-O, νTe-O-Te, and νTe-O-Te, while νN=O and δN=O were also detected at 1361 cm−1 and 1039 cm−1, respectively, indicating the presence of NO3− in the black substance. Synthesizing the experimental phenomena and literature data, the composition of the black substance was presumed to be xTeO2-Sb2O3-HNO3 (2 < x < 3), and the corresponding reaction chemical equation was given. This study provides an important reference for further optimization of the production process. [ABSTRACT FROM AUTHOR]

This paper proposes a technique to improve the performance of a thermoelectric element (TEE) using an external magnetic field. The influence of the external magnetic field is investigated with respect to the output electrical power and thermal efficiency of the TEE as a generator, while for the TEE as a cooler, the coefficient of performance, heat absorbed, temperature of the cold side, and current input of the TEE are also examined. From analytical and numerical investigations carried out on bismuth telluride TE material, we reveal that the presence of the magnetic field significantly improves the performance of the TEE operating as a generator below the Curie temperature. Furthermore, in the case of the TEE operating as a generator, we observe a gain of about 75 % and 81.25 % corresponding to the electrical output power and thermal efficiency, respectively, whereas in the case of a TEE cooler, its coefficient of performance is significantly improved by 94.73 % . [ABSTRACT FROM AUTHOR]

Transition metal carbides (TMCs) have attracted the attention of many researchers as promising thermoelectric materials due to their excellent electrical, thermal, and chemical properties. Titanium carbide (TiC), a compound of titanium and carbon, is a valuable member of the family of TMCs; however, studies on the thermoelectric properties of this material are limited. In the present study, the effects of the addition of TiC on the thermoelectric properties of polypyrrole (PPy) were investigated for the first time. Firstly, TiC-filled PPy hybrid composites containing different weight ratios of TiC (0.5%, 1%, 3%, 5%, and 10% with respect to polymer) were prepared by in situ oxidative chemical polymerization. The composites were characterized using Fourier transform infrared-attenuated total reflectance spectroscopy, ultraviolet-visible spectroscopy, Brunauer–Emmett–Teller and Barrett-Joyner-Halenda methods, x-ray diffraction, and scanning electron microscopy (SEM). The electrical conductivity measurements indicated that the electrical conductivity significantly increased in direct proportion with the increasing amount of TiC and the electrical conductivity of the pristine PPy increased from 0.8 Scm−1 up to 160.2 Scm−1 with the addition of 10% TiC. Furthermore, the addition of TiC led to increase in the power factor from 0.0115 μW m−1K−2 to 1.732 μW m−1K−2 which is approximately 150 times higher than the pristine PPy. This study indicated that the addition of TiC remarkably contributed to the TE properties of PPy. [ABSTRACT FROM AUTHOR]

Thermoelectric materials can easily realize energy savings by converting untapped waste heat into electricity. Unfortunately, however, the coupling of the thermoelectric parameters limits the conversion efficiency. Herein, we fabricated titanium oxide ceramic thermoelectric materials using a simple one-step solid-state reaction between TiO2 and starch at high temperature, and improved the electrical and thermal transport properties simultaneously by adjusting the amount of starch during preparation. With increasing starch, the electrical conductivity and power factor increased and the thermal conductivity decreased significantly. The samples mixed with 7 wt% starch showed rather low thermal conductivity (less than 2.0 W m−1 K−1) and a dimensionless figure of merit (ZT) close to 0.14K at 973 K. When the samples were sintered in an argon atmosphere, the starch was carbonized in situ into carbon and provided a reducing atmosphere, leading to the appearance of oxygen vacancies in the lattice of titanium oxide. The oxygen vacancies increased with increasing starch in the mixture during preparation, which resulted not only in a narrower band gap of titanium oxide but also enhanced phonon scattering. [ABSTRACT FROM AUTHOR]

Hybrid composites are promising materials for producing high-performance thermoelectric (TE) materials by combining the superior properties of both components. This study was conducted to investigate the effects of boron carbide (B4C) on the TE performance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). TE studies demonstrated that the addition of B4C enhances the electrical conductivity of pristine PEDOT:PSS from 11.1 S cm−1 to 1083.8 S cm−1. Furthermore, the power factor of pristine PEDOT:PSS was enhanced from 0.25 μW m−1 K−2 up to 237 μW m−1 K−2. The obtained results indicate that B4C is a suitable additive for polymer-based TE composites. [ABSTRACT FROM AUTHOR]

High-purity bismuth telluride (Bi2Te3) nanostructures have been synthesized by a chemical reduction method with two processes: (1) co-precipitation by NaBH4 and (2) annealing under hydrazine vapor and nitrogen gas atmosphere at T = 300°C. Based on the use of nitric acid (HNO3) in the preparation of precursor solutions from primary materials, two syntheses were designed to prepare the Bi2Te3 nanostructures. Then, the structural, optical, and thermoelectric properties and the surface morphology of the obtained nanoparticles from the two syntheses were investigated. The X-ray diffraction analysis results revealed the formation of Bi2Te3 nanostructures in both syntheses. The values of the crystallite size and micro-strains of the Bi2Te3 nanostructure were obtained from the average Williamson–Hall (Langford) analysis and Scherrer methods. Field-emission scanning electron microscopy micrographs of the Bi2Te3 nanostructures showed hexagonal nanocrystals with different nano-sizes. Energy dispersive x-ray spectroscopy analysis confirmed the formation of the Bi2Te3 compound and the high purity of the synthesized nanostructures. The Bi2Te3 nanostructure produced in the second synthesis (HNO3-Bi&Te) had a higher Seebeck coefficient (56.3 μ V / K ) and lower resistance (9 k Ω ). The amount of ZT in this optimal synthesis (HNO3-Bi&Te) increased by 6.5 times. The results of the Seebeck experiment mostly showed p-type conductivity for the two syntheses. Fourier-transform infrared spectroscopy analysis showed very low absorption of the NH2 group on the Bi2Te3 nanostructured surface. This study showed that annealing in the presence of hydrazine vapor has major influences on the formation of the bismuth telluride binary phase. [ABSTRACT FROM AUTHOR]

Innovative material configurations obtained by incorporating two-dimensional (2D) layers of MoS2 (a two-dimensional material) with Fe doped ZnO (Fe:ZnO) thin films are found to exhibit high thermoelectric properties at lower temperature. The low dimensionality of material (MoS2) is expected to enhance the thermoelectric power factor because of the strong confinement of charge carriers. MoS2 layers have been incorporated in the Fe:ZnO thin film by depositing MoS2 layers over Fe:ZnO thin film and by fabricating the multilayered structure of MoS2 layers with Fe:ZnO. The fabricated structures were characterized for their structural, optical and morphological properties using the available characterization tools. The multilayer configuration of the MoS2 and Fe:ZnO (FZnMFZn) sample was found to exhibit higher values of power factor of 1.06 × 10−3 W/mK2 and figure of merit (ZT) of 3.11 × 10−2 at a very low operating temperature of 300 K. The obtained results highlight the importance of charge confinement in improving the thermoelectric properties of the multilayered structure (FZnMFZn thin film sample) indicating that it is a promising candidate for practical applications. [ABSTRACT FROM AUTHOR]

Bi2Te3 compound has been shown to exhibit the highest thermoelectric figure of merit at 573 K to 673 K. Bi2Te3 samples were synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS) in this work. The effects of the milling and SPS parameters as well as the specimen thickness were evaluated to obtain the best microstructural and thermoelectric properties. To synthesize Bi2Te3, Bi and Te powders were mechanically alloyed under argon atmosphere in a stainless-steel vial with a ball-to-powder weight ratio of 15:1 for different durations. The synthesized powders were then sintered using SPS at different temperatures. To characterize the Bi2Te3 powders and bulk samples, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analysis were applied. Furthermore, the bandgap energy was measured by ultraviolet–visible (UV–Vis) spectroscopy. Moreover, the Seebeck voltage and electrical conductivity were determined at different temperatures. The experimental results illustrate that, by enhancing the sintering temperature from 623 K to 673 K, the maximum Seebeck coefficient was increased from 136 μV/K to 156 μV/K. To investigate the effect of thickness, specimens were sintered at the optimum temperature of 673 K with thicknesses of 1 mm, 1.5 mm, 2 mm, 3 mm, and 4 mm. The results showed that, by decreasing the thickness, the maximum Seebeck coefficient was increased from 144 μV/K to 166 μV/K while the electrical conductivity was increased from 0.35 × 105 S/m to 1.42 × 105 S/m, resulting in an increase in the power factor from 0.76 mW/m-K2 to 3.94 mW/m-K2. [ABSTRACT FROM AUTHOR]

In the present study, thermoelectric properties of composites formed by poly (3,4-ethylenedioxy thiophene):poly (styrene-4-sulfonate) (PEDOT:PSS)/boron phosphate (BPO4) were studied. First, BPO4 was synthesized at 1000°C using boric acid and phosphoric acid as precursors. Later, PEDOT:PSS was synthesized by oxidative chemical polymerization reaction at room temperature. Their composites were prepared in different mass ratios by ultrasonic homogenization. The composites were characterized using ultraviolet–visible (UV–vis.), attenuated total reflection accessory attached Fourier transform infrared (FTIR-ATR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy/energy dispersive X-ray analyzer (SEM–EDX). The power factor of the sample was obtained using the electrical conductivity and Seebeck coefficient measurements. The positive sign of Seebeck coefficient of the pristine PEDOT:PSS turned to the negative, which is the characteristic of n-type material, by addition of BPO4. The power factor of PEDOT:PSS was increased from 0.03 μWm−1 K−2 to 252 μWm−1 K−2 for the composite containing 25% BPO4 by weight. This indicates that BPO4 can be a good additive to prepare n-type TE material. [ABSTRACT FROM AUTHOR]

The functionalization of graphene is a well-established route for modulating its optoelectronic properties for a wide range of applications. Here, we studied, using photoemission spectroscopies and synchrotron radiation, the band structure upon evaporation of a p-type dopant tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) molecules and determined the work function (WF) shift over a large area of epitaxial graphene grown on a 4H-SiC (0001) silicon carbide substrate. This system exhibits peculiar nanostructures composed of mono and multilayers, notably at the step edges where the electronic properties differ from the terraces. We observed, owing to the high spatial resolution of photoemission electron microscopy (PEEM), that after the adsorption of F4-TCNQ, multilayer graphene on step edges was subjected to less charge transfer compared to the monolayer graphene on terraces, making their final WF smaller. We calculated the thermoelectric properties of this functionalized graphene system by using density functional theory and Boltzmann transport formalism within the range of the Fermi level (EF), and the carrier concentration, which was experimentally determined. We show that the Seebeck coefficient (S) on the nanofacets is 25% larger than on the monolayer terraces, and the maximum power factor (PF) is on the order of 10−2 W/K2m. This order of magnitude is comparable to the PF of commercial thermoelectric materials such as bulk bismuth telluride. [ABSTRACT FROM AUTHOR]

Enhanced thermoelectric performances have been achieved in hybrid nanocomposites of TiO2 incorporated into electrically conductive polyaniline (PANI) through a chemical polymerization process, for next-generation energy sources. Different weight percentages of TiO2 were used in hybrid nanocomposites and their charge transport properties were studied to understand the consequence of TiO2 incorporation in the PANI matrix. Aniline was used as reactant, and ammonium peroxydisulfate as polymerizing agent during synthesis process. The hybrid composites of TiO2 incorporated PANI were studied by using X-ray diffraction pattern, Fourier transform-infrared spectra and scanning electron microscopic images. The thermoelectric characteristics of this PANI-based composite were much improved as compared to pure PANI. The ordered chain structures of PANI, and the decrease of carrier hopping barrier with incorporation of TiO2 nanoparticles in the PANI chain matrix improved the charge carrier conduction and lead towards enhanced thermoelectric properties of these materials. The maximum Seebeck coefficient (S) as recorded 1.767 mV/°C, was fivefold larger as compared with pure PANI. The analysis of results reveal that these hybrid composites are potential candidates for next-generation thermoelectric generators with their light weight, environmentally friendly nature and cost-effectiveness for energy harvesting applications. [ABSTRACT FROM AUTHOR]

SnxBi0.5-xSb1.5Te3 materials with high ZT values were prepared by vacuum melting, ball milling, cold pressing and ambient pressure sintering. The effect of Sn doping amount on the thermoelectric performance of Bi0.5Sb1.5Te3 -based materials was investigated. The results showed that Sn doping increased the carrier concentration and DOS effective mass to improve the electrical conductivity and Seebeck coefficient, respectively, resulting in an increase in the power factor. Meanwhile, the reduction in lattice thermal conductivity was attributed to enhanced phonon scattering. The decrease in bipolar thermal conductivity was caused by the suppression of intrinsic excitation. Finally, compared with Bi0.5Sb1.5Te3, the power factor increased 66%, to 2.72 mW·m−1·K−2, lattice thermal conductivity decreased by 28% to 0.334 W·m−1·K−1, and the ZT value for Sn0.01Bi0.49Sb1.5Te3 at 350 K was 1.33. [ABSTRACT FROM AUTHOR]

This work investigates the thermoelectric and electrical performance of nanostructured thin films of antimony (Sb)-doped Bi2Te3 (thickness ∼ 60 nm) and Bi0.5Sb1.5Te3 (thickness ∼ 60 nm). The films were deposited on a glass substrate by thermal evaporation under high vacuum conditions. The structure and morphology of the films was investigated by standard characterization techniques. X-ray diffraction was used to identify the formation of different phases during the synthesis of the films. The Van der Pauw and Harman methods were employed to measure the conductivity (σ) and figure of merit (ZT). Further, samples were subjected to annealing under a high vacuum at 200°C for 1 h to improve the quality and ZT of the deposited films. The Sb-doped Bi2Te3 film was found to be ∼ 6.5 times more conductive than the Bi0.5Sb1.5Te3 film. However, the two films exhibited comparable ZT values owing to the small value of the Seebeck coefficient (S) of Sb. This study represents a significant contribution in the field of thermoelectric materials and device applications. [ABSTRACT FROM AUTHOR]

Using improved extrusion technology for bismuth antimony tellurides, RMT has developed new extruded thermoelectric materials (TEM) with increased thermoelectric figure of merit (Z). The p-type materials exhibit maximum Z values of 3.28 × 10−3 K−1 to 3.32 × 10−3 K−1 in the electrical conductivity range from 900 Ω−1 cm−1 to 1100 Ω−1 cm−1. The corresponding Z values for the n-type materials lie in the similar range of 2.82 × 10−3 K−1 to 2.87 × 10−3 K−1. The wide variation of the electrical conductivity allows their application in miniature thermoelectric coolers (TEC) for cooling and temperature stabilization in the temperature range from 225 K to 350 K. Using the improved TEM, miniature TECs with pellet height of 0.3 mm were manufactured and tested; the test results showed that the maximum temperature difference was 2 K to 3 K higher while the energy consumption was 10% to 15% lower than for standard RMT miniature TEC. [ABSTRACT FROM AUTHOR]

Ni-doped tetrahedrites Cu12−xNixSb4S13 (x = 0.1–0.4) were prepared by mechanical alloying (MA) and sintered by hot pressing (HP). The tetrahedrite phase could be synthesized by MA without post-annealing, and was stable after HP without phase transition. As the Ni content increased, the lattice constant decreased from 1.0312 nm to 1.0246 nm, confirming that the Ni was successfully substituted for Cu sites. As the Ni content increased, the Seebeck coefficient increased but the electrical conductivity decreased because the carrier (hole) concentration decreased owing to the substitution of Ni2+ at the Cu+ site. The power factor of 1.0 mW m−1 K−2 was obtained at 723 K for the Ni-doped specimen with x = 0.1, and decreased with increasing Ni content. In addition, as the Ni content increased, the electronic thermal conductivity decreased, but the total thermal conductivity of the specimen with Ni content x = 0.2 showed the lowest value of 0.65–0.79 W m−1 K−1 at 323–723 K owing to the lowest lattice thermal conductivity of 0.38 W m−1 K−1 at 723 K. As a result, the dimensionless figure of merit ZT = 0.92 was obtained at 723 K for Cu11.8Ni0.2Sb4S13. [ABSTRACT FROM AUTHOR]

Based on naphthalene diimide (NDI), an alkylated naphthalene NDI with flexible side-chains was synthesized as a potential thermoelectric material. Then, n-type NDI/single-walled carbon nanotubes (SWCNT)-triethylamine composite films with different mass ratios of NDI to SWCNTs were prepared by drop-casting. The structures and properties of the composites were characterized by Raman spectroscopy, x-ray diffraction, ultraviolet–visible (UV–Vis) spectroscopy, scanning electron microscope, and transmission electron microscope, which indicated that strong interfacial interactions existed between NDI and SWCNTs. It was found that the NDI/SWCNT-triethylamine composite with an NDI to SWCNTs mass ratio of 1:1 exhibits a power factor of 34.9 μWm−1 K−2 at room temperature, and when the temperature rises to 418 K, the maximum value of the power factor reaches 64.9 μWm−1 K−2. These results demonstrate an effective way to enhance thermoelectric performance by improving interactions at organic and inorganic interfaces, which can also broaden the research scope of composite thermoelectric materials. [ABSTRACT FROM AUTHOR]

The analytical expressions derived using simple models provide clear insights on the processes in thermoelectric coolers. The model of constant transport coefficients (CTC) considers that the thermal conductivity, the electrical resistivity and the Thomson coefficient are constants. The version of the CTC model that has become standard in the description of the global energy balance may yield grossly inaccurate predictions for thermoelectric cooling applications. We show that these failures can be avoided by accurately describing the Thomson effect in the energy balance. Calculations for bismuth telluride semiconductors show that deviations as large as a factor of three in the Thomson power contribution to the global balance may be found under conditions of practical interest. Compared to the standard version (valid only for moderate temperature gradients), the improved version (valid for highly nonlinear temperature distributions) of the CTC model predicts that a larger fraction of the power released by the electric current leaves the thermoelectric element through the hot boundary. Significant differences in the estimations of the cooling capacity and the coefficient of performance of the thermoelectric cooler are also observed. [ABSTRACT FROM AUTHOR]

Electromotive force is generated by a temperature difference in a thermocouple formed of two different metals, known as the Seebeck effect. Flexible thermoelectric (TE) temperature sensors based on the Seebeck effect can be attached to the body to provide body temperature information to health providers via wireless communications. Materials used in flexible TE temperature sensors have higher Seebeck coefficients than those of traditional thermocouples, and hence generate a high output voltage even with small temperature changes, making them highly suitable for use as body temperature sensors. In this study, a flexible TE temperature sensor was fabricated using a cheap, commercial flexible printed circuit board substrate and TE thin films of n-type bismuth telluride and p-type antimony telluride by co-evaporation. The results show that the flexible TE temperature sensor has a sensitivity of 192.70 μV K−1. [ABSTRACT FROM AUTHOR]

Bismuth telluride (Bi2Te3) thin films have been deposited onto polyimide sheet substrates by direct-current (DC) magnetron sputtering at different powers and their microstructure, composition, and electrical and thermoelectrical properties studied. The experimental results indicated that the sputtering power was the key parameter determining their thermoelectric properties. X-ray diffraction analysis confirmed the highly (015) preferred orientation of the films. The Te content and grain size depended on the sputtering power. The power factor of Bi2Te3 deposited by DC sputtering at power of 60 W was comparable to that obtained for highly (00l) Bi2Te3 thin film. [ABSTRACT FROM AUTHOR]

Bi2Te3 nanoparticles (NPs) were synthesized with controlled mean diameters of 58 nm, 82 nm, and 100 nm using an aqueous chemical reduction, in which ascorbic acid was used instead of the commonly employed toxic reducing agent. In general, organic capping agents remained on the Bi2Te3 NP surfaces, which prevented the sintering of Bi2Te3 NPs and affected their thermoelectric properties. Not only the capping agent, but also water from the synthesis process, remained on the Bi2Te3 NPs even after their consolidation by spark plasma sintering. Consequently, evaporation of the water led to the collapse of sintered Bi2Te3 NPs when heated above 100°C. After the complete removal of the surface impurities and water, the sintered Bi2Te3 NPs became stable. To achieve enhanced thermoelectric properties, a high relative density of ∼ 96% was achieved in the sintered Bi2Te3 NPs without large grain growth by optimizing the sintering temperature and holding time. Subsequently, their thermoelectric properties showed that zT of the sintered Bi2Te3 NPs 100 nm in size is higher (0.41 at 390 K) than those of smaller sizes (58 nm and 82 nm). Finally, the effect of grain size, particle size and density on their thermoelectric properties is discussed. [ABSTRACT FROM AUTHOR]

Polycrystalline thermoelectric elements of n-type Bi2(Te0.95Se0.05)3 and p-type (Bi0.25Sb0.75)2Te3 were fabricated by modified Bridgman technique, followed by electrospark cutting. A thermoelectric micromodule, consisting of 12 legs with an Ni anti-diffusion barrier and high-temperature SnSb solder between them, was assembled. To investigate thermoelements under conditions close to operating ones, the micromodule was annealed at 443 K for 1000 h. It was revealed that after annealing for more than 40 h, the near-contact zone of the n-type legs degraded, leading to a complete break of the micromodule junctions. Our results revealed that during annealing, the SnSb solder flowed into the unprotected side surface of the legs, and contacted with the cleavage planes along which tin can diffuse into the thermoelement volume. In contrast, the p-type legs were not affected by the contact with the solder. Different impacts of the solder on n- and p-type legs were explained in the framework of density functional theory (DFT) calculations. Substitution, diffusion and thermodynamic stability calculations showed that Bi to Sn substitution is energetically more beneficial than Sb to Sn substitution. Additionally, it was calculated that for the Bi2Te3 + Sn system, it is more beneficial to form a TeSn and Bi phase, while an Sb2Te3 + Sn system is thermodynamically stable. [ABSTRACT FROM AUTHOR]

Waste heat recovery, using thermoelectric power technology, is a promising approach to reduce fuel consumption and CO2 emissions on passenger cars. However, possible application requires optimizing heat exchangers and defining adequate thermoelectric materials to improve efficiency. A dynamic model has been developed to investigate the application of a thermoelectric generator (TEG) for waste heat recovery in an automotive engine exhaust. The converted electrical energy is used to charge a 12 V battery. The model evaluates the amount of recovered energy over a prescribed drive-cycle. It also evaluates the effect of system integration on the TEG performances, such as fuel consumption, temperatures downstream of the TEG and the relative counter pressure. Experiments are done on both a thermoelectric module (TEM) test rig and a diesel engine test rig equipped with a TEG prototype. Simulations of steady operating points show good agreement with experimental data. The results show a maximum power of 42 W generated by the TEG, with a maximum power of 1.5 W per module (corresponding to TEM hot side temperature of 671 K and TEM cold side temperature of 354 K). At the end of the duty cycle, the energy recovered by the vehicle battery is around 27 kJ (7.5 Wh). The engine counter pressure exceeds 30 mbar when the mass flow rate is higher than 36 g s−1. The simulation results of temperatures, pressures, and output power show that the model can be used as a basis to develop a TEG with high performance that ensure safety operation of the engine and the after treatment system. [ABSTRACT FROM AUTHOR]

Doping is an effective approach to enhance the thermoelectric figure of merit (zT) of thermoelectric alloys by modifying their electronic structure. In this study, we investigated the influence of In doping on the electronic and thermal transport properties of n-type Cu0008Bi2-xInxTe2.7Se0.3 (x = 0, 0.005, 0.01, and 0.015) polycrystalline alloys. The electrical conductivity of the alloys showed a moderate decreased by In doping. The Seebeck coefficient also decreased slightly. The bandgap Eg of the alloys widened slightly according to the Goldsmid-Sharp Eg formula. The band parameters of the conduction and valence bands were estimated using a two-band model. In the case of the In-doped samples, the concentration and mobility of electrons decreased simultaneously, resulting in a reduction in the electrical conductivity. However, the level of bipolar conduction remained unchanged even after doping because of the compensation of Eg widening and the band parameter modification. Meanwhile, the effect of In doping on the thermal conductivity of n-type Cu0.008Bi2Te2.7Se0.3 was found to be insignificant. Consequently, the zT of the alloy increased slightly to 1.12 at x = 0.05, while it decreased at higher doping levels. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of devices based on bismuth telluride, skutterudite, and calcium manganese oxide have been investigated and compared using impedance spectroscopy at 23°C. Prior to the detailed analysis, Kramers-Kronig transformation tests were performed to examine the validity of the obtained impedance spectra. All the spectra were Kramers-Kronig transformable, and were interpreted using equivalent circuit fitting. The three key parameters (Seebeck coefficient, thermal conductivity, and electrical conductivity) and dimensionless figure of merit of bismuth telluride and skutterudite-based devices were successfully extracted from their respective impedance spectra. However, the thermal conductivity of the calcium manganese oxide-based device was overestimated, while the Seebeck coefficient and electrical conductivity values were reasonably accurate owing to their negligible thermoelectric effect at 23°C. We further proposed that the thermoelectric capacitance obtained from the impedance spectra could be a quantitative measure of the "propensity" of thermoelectric devices to generate thermoelectric power under an external temperature gradient. [ABSTRACT FROM AUTHOR]

Bismuth telluride (Bi2Te3) exhibits a transition from p- to n-type conduction as a result of high-energy ball milling. The transition is monitored over mechanical activation through measurement of the thermoelectric properties in the temperature range of 1.9 K to 390 K. Data show a flip in polarity of the Seebeck coefficient from 225 μV K−1 for the bulk sample to − 120 μV K−1 (at 315 K) that correlates to fracturing the layered-like structure of stoichiometric Bi2Te3 into platelets and fine particles. The electronic transition is generated by fracturing the crystal 90° to the basal plane. This is the structural equivalent to inducing n-type, anti-site defects on grain boundaries. The observed phenomenon could be exploited to fabricate p- and n-type legs for thermoelectric devices from the same material. In this report, we demonstrate that the value of the Seebeck coefficient for bismuth telluride can be tuned using mechanical treatment. We also determine how mechanical activation of Bi2Te3 impacts physical properties of the system, including: particle size, crystal structure, band gap, electrical and thermal conductivity, carrier concentration and mobility, average hopping distance, and the concentration of localized charged centers. [ABSTRACT FROM AUTHOR]

Bismuth telluride (Bi2Te3), traditionally used in the industry as thermoelectric material, has deserved much attention recently due to its properties as a topological insulator, a kind of material that might have relevant applications in spintronics or quantum computing, among other innovative uses. The preparation of high-quality material has become a very important technological task. Here, we compare the preparation of Bi2Te3 by physical vapor transport from the evaporation of elemental Bi and Te sources, under either low pressure or atmospheric pressure. The layers were characterized by different techniques to evaluate its structural properties. As a result, it is concluded that, as a consequence of the different transport regimes, films grown at atmospheric pressure present better crystal quality. [ABSTRACT FROM AUTHOR]

Camping lamps have been widely used in the lighting, power supply, and intelligent electronic equipment fields. However, applications of traditional chemical and solar camping lamps are largely limited by the physical size of the source and operating conditions. A new prototype multifunctional portable Bi2Te3-based thermoelectric camping lamp (TECL) has been designed and fabricated. Ten parallel light-emitting diodes were lit directly by a Bi2Te3-based thermoelectric generator (TEG). The highest short-circuit current of 0.38 A and open-circuit voltage of 4.2 V were obtained at temperature difference of 115 K. This TECL is attractive for use in multifunctional and extreme applications as it integrates a portable heat source, high-performance TEG, and power management unit. [ABSTRACT FROM AUTHOR]

During the past few decades, Bi2Te3-based alloys have been investigated extensively because of their promising application in the area of low temperature waste heat thermoelectric power generation. However, their thermal stability must be evaluated to explore the appropriate service temperature. In this work, the thermal stability of zone melting p-type (Bi, Sb)2Te3-based ingots was investigated under different annealing treatment conditions. The effect of service temperature on the thermoelectric properties and hardness of the samples was also discussed in detail. The results showed that the grain size, density, dimension size and mass remained nearly unchanged when the service temperature was below 523 K, which suggested that the geometry size of zone melting p-type (Bi, Sb)2Te3-based materials was stable below 523 K. The power factor and Vickers hardness of the ingots also changed little and maintained good thermal stability. Unfortunately, the thermal conductivity increased with increasing annealing temperature, which resulted in an obvious decrease of the zT value. In addition, the thermal stabilities of the zone melting p-type (Bi, Sb)2Te3-based materials and the corresponding powder metallurgy samples were also compared. All evidence implied that the thermal stabilities of the zone-melted (ZMed) p-type (Bi, Sb)2Te3 ingots in terms of crystal structure, geometry size, power factor (PF) and hardness were better than those of the corresponding powder metallurgy samples. However, their thermal stabilities in terms of zT values were similar under different annealing temperatures. [ABSTRACT FROM AUTHOR]

Cu0.003Bi0.4Sb1.6Te3 alloys were prepared by using encapsulated melting and hot extrusion (HE). The hot-extruded specimens had the relative average density of 98%. The (00l) planes were preferentially oriented parallel to the extrusion direction, but the specimens showed low crystallographic anisotropy with low orientation factors. The specimens were hot-extruded at 698 K, and they showed excellent mechanical properties with a Vickers hardness of 76 Hv and a bending strength of 59 MPa. However, as the HE temperature increased, the mechanical properties degraded due to grain growth. The hot-extruded specimens showed positive Seebeck coefficients, indicating that the specimens have p-type conduction. These specimens exhibited negative temperature dependences of electrical conductivity, and thus behaved as degenerate semiconductors. The Seebeck coefficient reached the maximum value at 373 K and then decreased with increasing temperature due to intrinsic conduction. Cu-doped specimens exhibited high power factors due to relatively higher electrical conductivities and Seebeck coefficients than those of undoped specimens. A thermal conductivity of 1.00 Wm−1 K−1 was obtained at 373 K for Cu0.003Bi0.4Sb1.6Te3 hot-extruded at 723 K. A maximum dimensionless figure of merit, ZTmax = 1.05, and an average dimensionless figure of merit, ZTave = 0.98, were achieved at 373 K. [ABSTRACT FROM AUTHOR]

Bismuth-telluride (BiTe)-based compounds are common thermoelectric materials used for low-temperature applications, and nickel (Ni) is usually deposited on the BiTe substrates as a diffusion barrier. Deposition of Ni on the p-type (Sb-doped) and n-type (Se-doped) BiTe substrates using electroplating and interfacial reactions between Sn and Ni-coated BiTe substrates are investigated. Electrodeposition of Ni on different BiTe substrates is characterized based on cyclic voltammetry and Tafel measurements. Microstructural characterizations of the Ni deposition and the Sn/Ni/BiTe interfacial reactions are performed using scanning electron microscopy. A faster growth rate is observed for the Ni deposition on the n-type BiTe substrate which is attributed to a lower activation energy of reduction due to a higher density of free electrons in the n-type BiTe material. The common NiSn phase is formed at the Sn/Ni interfaces on both the p-type and n-type BiTe substrates, while the NiTe phase is formed at a faster rate at the interface between Ni and n-type BiTe substrates. [ABSTRACT FROM AUTHOR]

Segmented generators where the p- or n-type legs are formed by joining materials in series enables each material to operate in their most efficient temperature range. Here, we have fabricated and characterized segmented thermoelectric p- and n-type legs based on bismuth tellurides and half-Heusler alloys p-type HfZrCoSnSb and n-type TiHfNiSn. A two-step process was introduced to join the half-Heusler to the bismuth tellurides to form a segmented structure which was then characterized for its thermoelectric and structural properties. The output power generation was characterized under various hot side temperatures up to 873 K with the cold side fixed at 323 K. The stability of the joints was also investigated under heat treatment and thermal cycling. Under working temperatures from 323 K to 873 K, the obtained p-type segmented legs could deliver a power density of 0.3 W cm and maximum voltage of 115 mV. With the same condition, the power density and the maximum voltage generated by n-type segmented leg were 0.25 W cm and 102 mV. The area-specific contact resistances of the p- and n-type legs were 50 μΩ cm and 35 μΩ cm, respectively. The output performance of each leg was ∼ 95% after 6 cycles from 323 K to 873 K. [ABSTRACT FROM AUTHOR]

BiTe compound and BiTe-based solid solutions have attracted much attention as promising thermoelectric materials for refrigerating devices. The possibility of enhancing the thermoelectric efficiency in low-dimensional structures has stimulated studies of BiTe thin films. Now, interest in studying the transport properties of BiTe has grown sharply due to the observation of special properties characteristic of three-dimensional (3D) topological insulators in BiTe. One of the possible manifestations of quantum size effects in two-dimensional structures is an oscillatory behavior of the dependences of transport properties on film thickness, d. The goal of this work is to summarize our earlier experimental results on the d-dependences of transport properties of BiTe thin films obtained by thermal evaporation in a vacuum on glass substrates, and to present our new results of theoretical calculations of the oscillations periods within the framework of the model of an infinitely deep potential well, which takes into account the dependence of the Fermi energy on d and the contribution of all energy subbands below the Fermi level to the conductivity. On the basis of the data obtained, some general regularities and specificity of the quantum size effects manifestation in 3D topological insulators are established. [ABSTRACT FROM AUTHOR]

Thermoelectric micro-coolers based on bismuth telluride (BiTe) and antimony telluride (SbTe) are important in many practical applications thanks to their compactness and fluid-free circulation. In this paper, we studied thermoelectric properties of bismuth/antimony telluride (Bi/SbTe) thin films prepared by the thermal co-evaporation method, which yielded among the best thermoelectric quality. Different co-evaporation conditions such as deposition flux ratio of materials and substrate temperature during deposition were investigated to optimize the thermoelectric figure␣of merit of these materials. Micron-size refrigerators were designed and fabricated using standard lithography and etching technique. A three-layer structure was introduced, including a p-type layer, an n-type layer and an aluminum layer. Next to the main cooler, a pair of smaller Bi/SbTe junctions was used as a thermocouple to directly measure electron temperature of the main device. Etching properties of the thermoelectric materials were investigated and optimized to support the fabrication process of the micro-refrigerator. We discuss our results and address possible applications. [ABSTRACT FROM AUTHOR]

BiTeSe:I ( y = 0.15-0.6 and m = 0.0025-0.01) solid solutions were prepared by mechanical alloying and hot pressing. The lattice constants that were measured from x-ray diffraction patterns decreased linearly with increasing Se content, but they were not changed remarkably by I doping. The average relative densities of the hot-pressed specimens are higher than 97%. All of the specimens exhibited n-type conductions in the measured temperature range from 323 K to 523 K, and their electrical conductivity decreased slightly with increasing temperature, indicating degenerate semiconductor behaviors. The electrical conductivity decreased with increasing Se content, whereas it was increased by I doping, and this is in contrast with the Seebeck coefficient; this resulted from the changes of the electron concentrations due to the Se substitution and the I doping. The thermal conductivity decreased with increasing Se content, and this is the result of both the decreased electronic thermal conductivity due to the decreased carrier concentration and the decreased lattice thermal conductivity due to the increased alloy scattering. The maximum dimensionless figure of merit for BiTeSe, ZT = 0.84 at 473 K, is due to its low thermal conductivity and high Seebeck coefficient. [ABSTRACT FROM AUTHOR]

The phonon and carrier thermal conductivities of thermoelectric materials were calculated using the Wiedemann-Franz law, Boltzmann equation, and a method we propose in this study called the Debye specific heat method. We prepared polycrystalline n-type doped bismuth telluride (BiTe) and bismuth antimony (BiSb) bulk alloy samples and measured six parameters (Seebeck coefficient, resistivity, thermal conductivity, thermal diffusivity, magneto-resistivity, and Hall coefficient). The carrier density and mobility were estimated for calculating the carrier thermal conductivity by using the Boltzmann equation. In the Debye specific heat method, the phonon thermal diffusivity, and thermal conductivity were calculated from the temperature dependence of the effective specific heat by using not only the measured thermal conductivity and Debye model, but also the measured thermal diffusivity. The carrier thermal conductivity was also evaluated from the phonon thermal conductivity by using the specific heat. The ratio of carrier thermal conductivity to thermal conductivity was evaluated for the BiTe and BiSb samples, and the values obtained using the Debye specific heat method at 300 K were 52% for BiTe and <5.5% for BiSb. These values are either considerably larger or smaller than those obtained using other methods. The Dulong-Petit law was applied to validate the Debye specific heat method at 300 K, which is significantly greater than the Debye temperature of the BiTe and BiSb samples, and it was confirmed that the phonon specific heat at 300 K has been accurately reproduced using our proposed method. [ABSTRACT FROM AUTHOR]

In this work, we fabricated BiSbTe thermoelectric alloys using the mass-production technique, and subsequently FeO and Fe-85Ni alloy nanoparticles were dispersed in the matrix by high energy ball milling and consolidated using spark plasma sintering technique. The influence of FeO and Fe-85Ni alloy spherical nanoparticles in BiSbTe (BST) matrix on thermoelectric transport properties has been investigated. The x-ray diffraction and scanning electron microscopy results show that the nanoparticles were dispersed in the matrix. The spark plasma sintered bulk BST/FeO composite sample exhibited high Seebeck coefficient which was 39% higher than the bare BST due to low carrier concentration and a significant reduction in the thermal conductivity (38%) owing to enhanced carrier scattering by the dispersed nanoparticles compared to that of the bare BST sample. As a result, the maximum ZT values for the BST, BST/FeO, and BST/Fe-85Ni samples were found as 1.17, 0.98, and 0.88 at 375 K, respectively. Micro Vickers hardness of BST/FeO and BST/Fe-85Ni composite samples was significantly enhanced compared to bare BiSbTe sample. [ABSTRACT FROM AUTHOR]

Printing technology is expected to provide innovative and environmentally friendly processes for thermoelectric (TE) module fabrication. As described in this paper, we propose an orientation control process using plastic deformation at high temperatures and present high-oriented TE nano-bulks fabricated from bismuth telluride (Bi-Te) TE inks using this process. In the case of n-type Bi-Te, surface x-ray diffraction reveals that crystalline grains in the plastic-deformed nano-bulk demonstrate a c-plane orientation parallel to the pressed face. According to the high orientation, electrical resistivity ρ, thermal conductivity κ, and figure of merit ZT show anisotropic behavior. It is noteworthy that ( ZT) almost reaches unity ( ZT) ∼1 at 340 K, even at low temperatures of the plastic deformation process. In contrast, the ZT of plastic-deformed p-type nano-bulk indicates isotropic behavior. The difference in the process temperature dependence of ZT suggests that n-type and p-type nano-bulk orientation mechanisms mutually differ. [ABSTRACT FROM AUTHOR]

Bismuth telluride alloys are promising thermoelectric materials used for portable␣and wearable cooling devices due to their excellent thermoelectric properties near the ambient temperature. Here, a simple and cost-effective brush-printing technique, together with a subsequent annealing treatment, has been used to prepare BiTe-based thick films and prototype devices. The composition, microstructure, and electrical properties of the brush-printed p-type BiSbTe thick films at different annealing temperatures are investigated. It is found that annealing temperature plays an important role in promoting densification and preventing the film from cracking, hence improving the electrical transport properties. The maximum power factor of the brush-printed thick films is 0.15 mW K m when annealed at 673 K for 4 h. A prototype thermoelectric device is manufactured by connecting the brush-printed p-type BiSbTe and n-type BiTeSe thick films with Cu thick-film electrodes on an AlO substrate. The cooling performance of the thermoelectric device is evaluated by measuring the temperature difference produced under applied currents. [ABSTRACT FROM AUTHOR]

Single-phase BiTe nanostructures (spherical and flower-like) have been synthesized using a modified hydrothermal method at different reaction temperatures (70°C, 100°C, and 150°C) and subsequently consolidated by spark plasma sintering. Their crystal structure, morphology, and thermoelectric and mechanical properties were investigated. The results suggest that the reaction temperature had a significant effect on the morphology and thermoelectric properties. The presence of nanostructures in bulk samples led to a remarkable decrease in thermal conductivity with a lesser effect on electrical conductivity. As a result, the figure␣of merit ( ZT) of the spark-plasma-sintered sample processed from spherical nanoparticles reached 0.54 at 400 K. The Vickers microhardness of the bulk sample processed from spherical nanoparticles was higher than the best results found in literature. [ABSTRACT FROM AUTHOR]

BiTe-based compounds are used practically as thermoelectric cooling materials. BiTe-SbTe or BiTe-BiSe 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 BiTe-based compounds have been reported in literature. Moreover, the detailed corrosion behavior of BiTe-based compounds remains unclear. In this study, the corrosion behavior of cleavage planes of BiTe-based compounds fabricated by a melting method has been investigated. BiTe, SbTe, and BiSe 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 BiTe and SbTe exhibited similar corrosion potential. The corrosion potential of c-plane of BiSe was more cathodic compared with that of the telluride. The passive current density of the BiTe-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 SbTe and BiSe. [ABSTRACT FROM AUTHOR]

This study explores a method of generating electricity while recovering waste heat through the integration of heat pipes and thermoelectric generators (i.e. HPTEG system). The simultaneous waste heat recovery and power generation processes are achieved without the use of any moving parts. The HPTEG system consists of bismuth telluride thermoelectric generators (TEG), which are sandwiched between two finned pipes to achieve a temperature gradient across the TEG for electricity generation. A counter-flow heat exchanger was built using two separate air ducts. The air ducts were thermally coupled using the HPTEG modules. The evaporator section of the heat pipe absorbed the waste heat in a hot air duct. The heat was then transferred across the TEG surfaces. The condenser section of the HPTEG collected the excess heat from the TEG cold side before releasing it to the cold air duct. A 2-kW electrical heater was installed in the hot air duct to simulate the exhaust gas. An air blower was installed at the inlet of each duct to direct the flow of air into the ducts. A theoretical model was developed for predicting the performance of the HPTEG system using the effectiveness-number of transfer units method. The developed model was able to predict the thermal and electrical output of the HPTEG, along with the rate of heat transfer. The results showed that by increasing the cold air velocity, the effectiveness of the heat exchanger was able to be increased from approximately 52% to 58%. As a consequence of the improved heat transfer, maximum power output of 4.3 W was obtained. [ABSTRACT FROM AUTHOR]

Over recent years, new thermoelectric materials have been developed with values for the dimensionless figure of merit, zT, substantially greater than unity. This has opened up the possibility of many new applications, particularly those involving the utilisation of waste heat. However, further improvements are necessary if thermoelectric generation is to have a significant impact on the world's energy problems. It is well known that zT for a single energy band can be related to the Fermi energy and a parameter ( μ/λ ) ( m*/m), where μ is the carrier mobility, m*/m is the ratio of the carrier effective mass to the mass of a free electron and λ is the lattice thermal conductivity. However, even when this parameter tends towards infinity, zT does not become much greater than 1 unless the Fermi level lies within the energy gap, far from the appropriate band edge. Thus, the magnitude of the energy gap is becoming of increasing importance. The two-fold requirements of a high value of ( μ/λ ) ( m*/m) and a sufficiently large energy gap are discussed. It is also shown that the likelihood of the required conditions being met at elevated temperatures can be predicted from low-temperature observations. It is, of course, much more difficult to make accurate determinations of the thermoelectric properties at higher temperatures. [ABSTRACT FROM AUTHOR]