Comprehensive study of tellurium based glass ceramics for thermoelectric application

Tellurium based glasses have interesting thermoelectric characteristics. However, their high electrical resistivity is still an obstacle to considering them for thermoelectric applications. In this work, the (Te₈₅Se₁₅)_60???0.6xAs_40???0.4xCu_x glass system was studied. This revealed that Cu can act as glass former and increase both glass thermal stability and electrical conductivity. The best candidate, (Te₈₅Se₁₅)₄₅As₃₀Cu₂₅, was chosen to prepare composites with Bi_0.5Sb_1.5Te₃ using spark plasma sintering. These glass ceramic samples exhibited a much better thermoelectric performance. Glass ceramics with 50?mol. % of Bi_0.5Sb_1.5Te₃ show a maximum ZT value equal to 0.37 at 413?K. Meanwhile, the advantages of glass including low sintering temperature and high formability are well maintained.     

Fabrication and electrical properties of Bi2-xSbxTe3 ternary nanopillars array films

Highly oriented Bi_2-xSb_xTe₃ (x?=?0, 0.7, 1.1, 1.5, 2) ternary nanocrystalline films were fabricated using vacuum thermal evaporation method. Microstructures and morphologies indicate that Bi_2-xSb_xTe₃ films have pure rhombohedral phase with well-ordered nanopillars array. Bi, Sb and Te atoms uniformly distributed throughtout films with no precipitation. Electrical conductivity of Bi_2-xSb_xTe₃ films transforms from n-type to p-type when x?>?1.1. Metal-insulator transition was observed due to the incorporation of Sb in Bi₂Te₃. Bi_2-xSb_xTe₃ film with x?=?1.5 exhibits optimized electrical properties with maximum electrical conductivity σ of 2.95?×?10⁵ S?m^?1 at T?=?300?K, which is approximately ten times higher than that of the undoped Bi₂Te₃ film, and three times higher than previous report for Bi_0.5Sb_1.5Te₃ films and bulk materials. The maximum power factor PF of Bi_0.5Sb_1.5Te₃ nanopillars array film is about 3.83?μW?cm^?1 K^?2 at T?=?475?K. Highly oriented (Bi,Sb)₂Te₃ nanocrystalline films with tuned electronic transport properties have potentials in thermoelectric devices.     

Hydrothermal method for the synthesis of Sb2Te3, and Bi0.5Sb1.5Te3 nanoplates and their thermoelectric properties

In this study, a modified hydrothermal method is reported for the preparation of Sb₂Te₃ and Bi_0.5Sb_1.5Te₃ nanoplates and their bulk samples was prepared by spark plasma sintering (SPS). The crystal structure, morphology, and thermoelectric properties were investigated. The microstructure results indicate that the bulk samples consisted nanograins after SPS. The presence of nanograins, high Seebeck coefficient (181 μV/K), high electrical conductivity (763 Ω^?1 cm^?1), and low thermal conductivity (1.15 W/mK) has been achieved in Sb₂Te₃ nanoplate bulk samples. As a result, the dimensionless thermoelectric figure of merit (ZT) of 0.55 at 400 K was achieved. Moreover, the peak ZT shifted to higher temperature compared with other reported results found in literature.     

Electrodeposition of P-type BixSb2−xTey thermoelectric film from dimethyl sulfoxide solution

The electrochemical behaviors of Bi(III), Te(IV), Sb(III) and their mixtures in DMSO solutions were investigated using cyclic voltammetry and linear sweep voltammetry measurements. On this basis, Bi_xSb_2−xTe_y film thermoelectric materials were prepared by potentiodynamic electrodeposition technique from mixed DMSO solution, and the compositions, structures, morphologies as well as the thermoelectric properties of the deposited films were also analyzed. The results show that Bi_xSb_2−xTe_y compound can be prepared in a very wide potential range by potentiodynamic electrodeposition technique in the mixed DMSO solutions. After anneal treatment, the deposited film prepared in the potential range of −200 to −400 mV shows the highest Seebeck coefficient (185 μV/K), the lowest resistivity (3.34 × 10⁻⁵ Ω m), the smoothest surface, the most compact structure and processes the stoichiometry (Bi_0.49Sb_1.53Te_2.98) approaching to the Bi_0.5Sb_1.5Te₃ ideal material most. This Bi_0.49Sb_1.53Te_2.98 film is a kind of nanocrystalline material and (0 1 5) crystal plane is its preferred orientation.     

Investigations on the electrodeposition behaviors of Bi0.5Sb1.5Te3 thin film from nitric acid baths

The electrochemical reduction process of Bi³⁺, HTeO₂⁺, Sb^III and their mixtures in nitric acid medium was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The reduction products electrodeposited at various potentials were examined using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The results show that cathodic process in the nitric acid solution containing Bi³⁺, HTeO₂⁺ and Sb^III involves the following reduction reactions in different polarizing potential ranges: In low polarizing potential ranges, Te⁰ is formed firstly on the electrode surface through the electrochemical reduction of HTeO₂⁺; with the negative shift of the cathodic polarizing potential, the reduction reaction of Bi³⁺ with Te⁰ to form Bi₂Te₃ takes place; when the cathodic polarizing potential is negative enough, Bi³⁺ and Sb^III react with Te⁰ to form Bi_0.5Sb_1.5Te₃. The results indicate that Bi_0.5Sb_1.5Te₃ films can be fabricated by controlling the electrodepositing potential in a proper high potential ranges.     

Enhancement in thermoelectric properties using a P‐type and N‐type thin‐film device structure

In this study, we have fabricated thermoelectric devices with p‐type and n‐type conducting polymers and research the effect of device structure with the thermoelectric properties. It was found that the p‐type and n‐type structure greatly enhances the device's electrical conductivity due to separated charge carrier channels, but the Seebeck coefficient was reduced due to the increase of charge density by doping. Photoexcitation can improve the device's thermoelectric properties and can increase the Seebeck coefficient and electrical conductivity with increasing doping concentration simultaneously. The increases in both properties are due to the phonon–electron coupling effect: the concentration of electrons and holes are increased under illumination, and the phonon component of the heat flux can be reduced by phonon scattering. Consequently, the thermoelectric device structure can improve the efficiency of thermoelectric conversion. The P3HT:PCBM devices demonstrate a significant enhancement in the power factor (PF = S²σ), with a maximum value of ZT = 0.5 at 147°C, in which the PF value (34.8 μV/cm K²) is bigger than Bi₂Te₃/Sb₂Te₃ superlattice devices at room temperature. POLYM. COMPOS., 34:1728–1734, 2013. © 2013 Society of Plastics Engineers     

Pulsed electrodeposition of (Bi1-xSbx)2Te3 thermoelectric thin films

(Bi_1-xSb_x)₂Te₃ thermoelectric thin films were deposited on stainless steel discs in 1 M perchloric acid and 0.1 M tartaric acid by pulse electrodeposition in order to optimize the grain growth. The influence of the electrolyte composition, the cathodic current density and the cathodic pulse time on film stoichiometry were studied. The results show that it is necessary to increase the Sb content in the electrolyte to obtain the (Bi_0.25Sb_0.75)₂Te₃ film stoichiometry. Pulse plating reduced the grain size and the roughness, compared with continuous plating. Thermoelectric and electrical properties were also studied and it was found that the Seebeck coefficient and electrical resistivity were related to two parameters: the cathodic pulse current density and the films thickness.     

Effect of Sintering Temperature on Thermoelectric Properties of p‐Bi2Te3 Alloys Produced by Gas Atomization

In this research, p‐type Bi₂Te₃–75% Sb₂Te₃ thermoelectric alloy powders were produced by gas atomization and subsequently sintered by hot pressing at different temperatures. The grain growth of the hot‐pressed samples was observed with increasing sintering temperature from 380°C to 460°C. The compressive strength increased with increasing hot‐pressing temperature due to the high relative density of bulk samples obtained at high temperatures. The effect of sintering temperature on thermoelectric (TE) properties was studied. The maximum power factor 3.48 mW/mK² was obtained for the sample hot pressed at 420°C due to the resulting high electrical conductivity and enhanced Seebeck coefficient values.     

Effect of PbTe on Thermoelectric Properties of Co<Subscript>0.88</Subscript>Ni<Subscript>0.12</Subscript>Sb<Subscript>2.91</Subscript>Sn<Subscript>0.09</Subscript>

The Co_0.88Ni_0.12Sb_2.91Sn_0.09 compound was synthesized by a metallurgical route, and PbTe powder was prepared by the low-temperature aqueous chemical method. Composite materials (xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09) were prepared by the ball-milling and the hot-pressed process. Electrical conductivities of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 hot-pressed samples decrease with increase of PbTe content, but their thermal conductivities were effectively improved due to induction of disperse phase. Due to agglomeration of the disperse phase, little thermal conductivity improvement occurs for composite material with low PbTe content. The ZT values of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 samples were hardly enhanced due to the negative contribution of electrical conductivity.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

A thermoelectric generator comprising selenium-doped bismuth telluride on flexible carbon cloth with n-type thermoelectric properties

Carbon cloth was used as a flexible substrate for bismuth telluride (Bi₂Te₃) particles to provide flexibility and improve the overall thermoelectric performance. Bi₂Te₃ on carbon cloth (Bi₂Te₃/CC) was synthesized via a hydrothermal reaction with various reaction times. After over 12 h, the Bi₂Te₃ particles showed a clear hexagonal shape and were evenly adhered to the carbon cloth. Selenium (Se) atoms were doped into the Bi₂Te₃ structure to improve its thermoelectric performance. The electrical conductivity increased with increasing Se-dopant content until 40% Se was added. Moreover, the maximum power factor was 1300 μW/mK² at 473 K for the 30% Se-doped sample. The carbon cloth substrate maintained its electrical resistivity and flexibility after 2000 bending cycles. A flexible thermoelectric generator (TEG) fabricated using the five pairs of 30% Se-doped sample showed an open-circuit voltage of 17.4 mV and maximum power output of 850 nW at temperature difference ΔT = 30 K. This work offers a promising approach for providing flexibility and improving the thermoelectric performance of inorganic thermoelectric materials for wearable device applications using flexible carbon cloth substrate for low temperature range application.     

Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Shift of tellurium solid-solubility limit and enhanced thermoelectric performance of bismuth antimony telluride milled with yttria-stabilized zirconia balls and vessels

As a thermoelectric material, Bi_0.3Sb_1.7Te_3.0+x (x = 0‒0.05) was fabricated by mechanical alloying using yttria-stabilized zirconia (YSZ) ceramic balls and vessels, followed by hot pressing. The effects of the added tellurium on the thermoelectric properties of Bi_0.3Sb_1.7Te_3.0 fabricated with YSZ milling media were investigated. All sintered samples were isotropic and showed p-type conduction. The tellurium solid-solubility limit for Bi_0.3Sb_1.7Te_3.0 was determined to be x = 0.01 by differential thermal analysis (DTA). The solid-solubility limit of the sample fabricated using YSZ was narrower than that of the congener prepared with Si₃N₄ balls and stainless-steel metal vessels. Among the evaluated compositions, the Bi_0.3Sb_1.7Te_3.01 sintered disk had the highest dimensionless figure of merit, ZT = 1.30, at room temperature. This value was superior to that of Bi_0.3Sb_1.7Te_3.0+x fabricated using metal vessels. Thus, selection of the milling media affected the optimum doping amount and maximum ZT.     

Recent progress in electrodeposition of thermoelectric thin films and nanostructures

Thermoelectric power generators and coolers have many advantages over conventional refrigerators and power generators such as solid-state operation, compact design, vast scalability, zero-emissions and long operating lifetime with no maintenance. However, the applications of thermoelectric devices are limited to where their unique advantages outweigh their low efficiency. Despite this practical confine, there has been a reinvigorated interest in the field of thermoelectrics through identification of classical and quantum mechanical size effects, which provide additional ways to enhance energy conversion efficiencies in nanostructured materials. Although, there are a few reports which demonstrated the improvement of efficiency through nanoengineering, the successful application of these nanostructures will be determined by a cost-effective and high through-put fabrication method. Electrodeposition is the method of choice to synthesize nanoengineered thermoelectric materials because of low operating and capital cost, high deposition rates, near room temperature operation, and the ability to tailor the properties of materials by adjusting deposition conditions. In this paper, we reviewed the recent progress of the electrodeposition of thermoelectric thin films and nanostructures including Bi, Bi_1−xSb_x, Bi₂Te₃, Sb₂Te₃, (Bi_1−xSb_x)₂Te₃, Bi₂Se₃, Bi₂Te_3−ySe_y, PbTe, PbSe, PbSe_1−xTe_x and CoSb₃.     

High thermoelectric performance achieved in Bi0.4Sb1.6Te3 films with high (00l) orientation via magnetron sputtering

To obtain p-type Bi–Sb–Te-based thin films with excellent thermoelectric performance, the Bi_0.4Sb_1.6Te₃ target is prepared by combining mechanical alloying with the spark plasma sintering technique. Afterward, Bi_0.4Sb_1.6Te₃ thin films are deposited via magnetron sputtering at variable working pressures. With an increasing working pressure, the frequency of collisions between the argon ions and sputtered atoms gradually increases, the preferred orientation of (00l) increases, and the sputtering rate decreases. The Seebeck coefficient increases from ∼140 μV/K to ∼220 μV/K as the carrier concentration decreases along with an increasing working pressure. Furthermore, the decrease in carrier concentration and acceleration of carrier mobility also affect the change in electrical conductivity. The maximum power factor of the p-type Bi_0.4Sb_1.6Te₃ thin film deposited at 4.0 Pa and at room temperature exceeds 20.0 μW/cm K² and is higher than that of most p-type Bi–Sb–Te-based films.     

Phase Diagram and Glass Formation in the Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-AgI System

The phase diagram, the glass formation, and the physicochemical properties of glass-forming and crystalline compositions in the Sb₂S₃-AgI system are investigated. Glasses in this system are moisture-resistant and have high refractive indices. These materials can be used in optical devices operating in the long-wavelength spectral range and as membranes for chemical sensors. The phase diagram of the Sb₂S₃-AgI system is constructed from the data of X-ray powder diffraction and differential thermal analyses.     

Glass formation and the phase diagram of crystalline components in the Sb<Subscript>2</Subscript>S<Subscript>3</Subscript>-PbI<Subscript>2</Subscript> system

Glasses in the Sb₂S₃-PbI₂ system are synthesized, and their physicochemical properties are investigated. The glasses possess high refractive indices (up to 3 or greater). The phase diagram of the Sb₂S₃-PbI₂ system is constructed from the data of differential thermal and X-ray powder diffraction analyses. The diagram exhibits an eutectic behavior. The eutectic is located at a content of 47 mol % PbI₂ and at a temperature of 370 ± 5°C.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Samoilenko, Mohammad Arif, Novikov, Filatov, Blinov.     

Triple phase structure and electron density analysis of the thermoelectric material Bi80Sb20

The thermoelectric material Bi₈₀Sb₂₀ was grown by high temperature melt-quench growth method and characterized by powder XRD. The Rietveld refinements revealed the presence of Bi₈₀Sb₂₀ and also the elemental parents Bi and Sb. All the three phases were analyzed and the electron density distribution and local structure of Bi, Sb and Bi₈₀Sb₂₀ were individually studied. The bonding between the atoms was studied using maximum entropy method (MEM). A comparison of 3D and 2D electron density distributions of Bi, Sb and Bi₈₀Sb₂₀ on the (110) and (024) planes clearly shows highly concentrated and localized electron clouds in Bi₈₀Sb₂₀ supporting the use of BiSb alloy as a thermoelectric material.     

Optimization of thermoelectric properties of metal‐oxide‐based polymer composites

Thermoelectric modules can be used for thermal energy harvesting. Common rigid thermoelectric stacks usually contain heavy metal alloys such as Bi₂Te₃. In order to substitute conventional materials and to reduce manufacturing costs, nontoxic, inexpensive and abundant materials using low‐cost processes are first choice. This study deals with polymer composites consisting of a polysiloxane matrix filled with thermoelectric Sn_0.85Sb_0.15O₂ particles in micrometer scale. Thin composite sheets have been prepared by doctor blade technique and the Seebeck coefficient, the electrical and thermal conductivity, and the porosity were measured. Platelet‐type particles, consisting of Sn_0.85Sb_0.15O₂‐coated insulating mica substrate and globular Sn_0.85Sb_0.15O₂ particles have been varied in size, coating thickness and were mixed with each other in different ratios. The filler content was varied in order to maximize the figure of merit, ZT, to 1.9 × 10^?5 ± 4 × 10^?6. Owing to their low raw material costs and the high degree of design freedom of polymer composites, one may use these materials in thermoelectric generators for remote low‐power demanding applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40038.     

Simple One-Pot Preparation of In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano-particles Using a Supramolecular 3D Framework Polymer

An indium(III) three-dimensional coordination framework, [In₂(OH)₃(O₄C₈H₄)_1.5] _n (1), was synthesized by hydrothermal method and characterized by elemental analyses, X-ray powder diffraction (XRD) and IR spectroscopy. Indium(III) oxide nanoparticles was prepared by direct thermal decomposition of 1 at 450 °C in air. The indium(III) oxide nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction (XRD) and energy-dispersive X-ray analysis (EDAX). This study demonstrates the coordination polymer frameworks may be suitable precursors for a simple one-pot preparation of nanoscale metal oxide materials with different and interesting morphologies.