Papers by Keyword: Bismuth Telluride

Abstract: Thermoelectric materials can directly convert thermal energy into electrical energy, realizing the recovery of waste heat. Bismuth Telluride (Bi-Te) is considered as a perfect candidate thermoelectric material which has great potential in the field of refrigeration and temperature sensor. However, in the field of intelligent wearable devices and integrated circuits, traditional Bi-Te block material is difficult to be directly used due to its poor flexibility. In this paper, a series of Bi-Te thin films were prepared by a self-designed high-temperature thermal shock equipment. This equipment can heat up the reduced graphene oxide strip to 1750 K in 20 ms, which features both high heating rate (8.2 × 10⁴ K/s) and cooling rate (1.5 × 10⁴ K/s). Thermoelectric films on different substrates were prepared via high-temperature thermal shock. Through regulating the temperature of evaporation source, the particle size and composition of Bi-Te thin films can be precisely modulated, thus optimizing the Seebeck coefficient of the films. The Seebeck coefficient of copper foil (Cu_f)-based Bi-Te film can reach 345.41 μV/K, which was prepared by thermal-shocking the Bi-Te powders for 30 s at 900°C.

Abstract: The world is currently facing numerous challenges related to energy supply and consumption. Renewable energy sources are very important in view to enhance the worldwide energy needs and environmental effects. One of the important, cost effective and pollution free techniques for renewable energy source is the thermoelectric technology. Thermoelectric materials are of great importance as they convert the heat energy into electrical energy. Thermoelectric materials include tellurides, cobaltites and oxides. In present work, bismuth telluride doped with rare earth metal Gadolinium of different compositions i.e. 0.0 and 0.1 was synthesized by using the simplified sol-gel technique. For structural analysis including crystal structure, phase purity, crystallite size of samples and the lattice parameters, X-ray diffraction (XRD) was used. The structural analysis showed the rhombohedral structure of Bi₂Te_3. AC electrical properties i.e. ac conductivity, loss factor, dielectric constant and impedance studied as a function of frequency (20Hz-3MHz). AC conductivity increased with the increase in frequency while the loss factor, dielectric constant and impedance decreased with the increase in frequency. DC resistivity was analyzed using two probe method at room temperature. Thermal transport properties i.e. thermal conductivity (λ), thermal diffusivity (κ) and volumetric heat capacity(ρCp) are also measured along with the Seebeck coefficient at room temperature.

Abstract: The Bi–Te thermoelectric system shows an excellent figure of merit (ZT) near room temperature. Research on increasing the ZT value for n‑type Bi–Te is imperative because the thermoelectric properties of this compound are inferior to those of the p-type material. For this purpose, n-type Bi₂Te_3-ySe_y powders with various amounts of Se dopant (0.3 ≤ y ≤ 0.6) were synthesized by a vacuum melting-grinding process to improve the physical properties. The ZT value of the sintered bodies was investigated in the temperature range of 298–423 K with regard to the electrical and thermal characteristics. As the Se content increased, the electrical conductivity decreased owing to a reduction in the carrier concentration, which improved the overall value of ZT. The thermal conductivity clearly decreased as the Se content increased in the temperature range of 298–373 K due to increased alloy scattering, as well as a reduction in the lattice thermal conductivity caused by crystal grain boundary scattering. At room temperature, Bi₂Te_2.7Se_0.3 (y = 0.3) exhibited the highest ZT of 0.85. At increased temperatures, the ZT value was highest for Bi₂Te_2.55Se_0.45 (y = 0.45), indicating that the optimal effect of the Se dopants varies depending on the temperature range.

Abstract: Thermoelectric (TE) nanogenerators are solid state devices that can directly convert thermal energy into electrical power. The family of bismuth telluride (BiTe)-based semiconductor materials is a good candidate for room-temperature thermoelectric applications. This work aims to synthesize the binary and ternary TE nanowire arrays from BiTe and BiSbTe using template-assisted electrochemical deposition. The compositions and lengths of the nanowires fabricated were precisely tuned by controlling the deposition conditions, while their diameters were confined by the pore sizes of the anodized alumina oxide (AAO) templates used. Chemical compositions of the nanowires were evaluated using Energy Dispersive X-ray (EDX) Spectroscopy and their microstructures were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), conventional transmission electron microscopy (CTEM) and high resolution transmission electron microscopy (HRTEM). TE nanogenerator modules comprising of BiTe and BiSbTe nanowires/AAO composite arrays were fabricated for TE performance evaluation on the basis of their power outputs.

Abstract: The research of magneto-optical properties has been conducted for the “Nanocomposite-bismuth telluride” (Co₄₀Fe₄₀B₂₀)_33.9(SiO₂)_66.1/[Te₃Bi₂] multilayer system at various thicknesses of each layer type. We report an enormous enhancement of magneto-optical (MO) response in this system. Besides, a good correlation between thickness dependences of transversal Kerr effect (TKE) and magneto-transport properties has been established. Such correlation was related to peculiarities of the interface forming process at the ferromagnetic (FM) granule boundaries. Moreover, this amplification of magneto-optical response is largest among the other spacer layers, such as Si, Cu, and C, therefore a comparison between them has been plotted.

Abstract: Recently, thermoelectric thin films have been gaining attention as potential thermoelectric generators that can be used to power external devices. Such films can recover electrical energy from waste heat and are environmentally friendly. Micro fabrication of thin films is achieved by sputtering on silicon films. In this study, the sputtering of Bismuth Telluride (N-type, P-type) films was investigated. Research has verified the efficiency of Bismuth Telluride films, but little is known about how the sputtering process affects the film's quality. Thus, the focus of this study explores how sputtering parameters of discontinuous sputtering intervals, exposure to normal atmospheric conditions and in situ annealing affect the thickness, thermoelectric properties, and microstructure of films. This will bring about a better understanding of the relationship between the sputtering process and the properties of the produced film for both N and P type materials. Recommendations based on this study can contribute to the production of more efficient thin films suitable for energy harvest application.

Abstract: Nanopowders of n-type (Bi0.95Sb0.05)2(Te0.95Se0.05)3 and p-type (Bi0.2Sb0.8)2Te3 have been synthesized by laser fracture of micron-sized powders in water. These alloys are the best conventional thermoelectric materials for use in room temperature applications. The nanopowders have been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanopowders have been mechanically mixed in different ratios with the micron sized powders. These mixtures have then been cold pressed in order to perform thermoelectric characterization and to see the influence of nano-particle inclusions on the transport properties.

Abstract: Prepared were p-type Bi2Te3-based thermoelectric semiconductors, having a grain-refined microstructure and a preferred orientation of anisotropic crystallographic structure. Disks with a nominal composition Bi0.5Sb1.5Te3.0 were cut from an ingot grown by the vertical Bridgman method (VBM) and deformed at 473 K under a pressure of 6.0 GPa by high pressure torsion (HPT). The crystal orientation was characterized with X-ray diffraction. The microstructures were characterized by using optical microscopy and scanning electron microscopy. It was found that the HPT disks had a fine and preferentially oriented grain compared to that of the VBM disks. Further, the power factor of the HPT disks was about twice as large as that of the VBM disks. These results indicate that HPT is effective for improving the thermoelectric properties of Bi2Te3-based thermoelectric semiconductors.

Abstract: The n-type Bi2Te2.7Se0.3 compounds were fabricated to investigate the characterization of spark plasma sintering with various SbI3 dopant contents. The Bi2Te2.7Se0.3 compounds with SbI3 dopant content is exhibited n-type conduction characterization, but the Bi2Te2.7Se0.3 compounds without SbI3 dopant content is exhibited p-type conduction characterization. The maximum Seebeck coeficient represented with 0.05wt.% SbI3 dopant content. The Seebeck coefficient of the sintered sample with increasing sintering temperature is increased from -158 to -182 μV/K. The electrical resistivity and thermal conductivity with 0.05wt.% SbI3 dopant content were 1.0 m and 1.33 W/mK, respectively.

Abstract: Using NaBH4 as reductant, Bi2Te3 nano-powders with different morphology such as nano-rod and nano-sphere were synthesized from BiCl3 and Te through an aqueous chemical method at temperatures below 100°C. The nano-rods were 100~200nm in diameter and 10~12μm in length, the diameter of the nano-spheres is between 100 and 500nm. The phase purity of the powders was analyzed by XRD, micro morphology and chemical compositions were characterized by SEM and EPMA. The reaction mechanism was discussed.