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[en] The request of thermoelectric materials for low-power and flexible applications fosters the investigation of the intrinsic electron and thermal transport of conducting polymeric chains, which are building blocks of the complex variety of organic composites proposed in experimental samples. Using calculations from first principles and the Landauer approach for both electron and phonon carriers, we study the thermoelectric figure of merit zT of three representative and largely used polymer chains, namely poly(3,4-ethylenedioxythiophene), polyaniline and polyfluorene. Our results provide an upper-limit estimate of zT , due to the intrinsic electronic and vibrational properties of the selected compounds, and pave the way to a microscopic understanding of the mechanisms that affect their electronic and transport characteristics in terms of structural distortions and chemical doping. (paper)
[en] Heat flow through a thermoelectric material or device can be varied by an electrical resistor connected in parallel to it. This phenomenon is exploited to design a novel thermal component-variable thermal resistor. The theoretical background to this novel application is provided and an experimental result to demonstrate its feasibility is reported. (fast track communication)
[en] We report significant enhancement in thermoelectric performance of n-type Bi2(Te,Se)3 prepared via conventional melting process. We deposited chemically synthesized Ag nanoparticles onto Te-rich Bi2(Te,Se)3 and sintered the resulting substance to obtain a bulk product. The Ag nanoparticles and excessive Te elements should be converted to interstitial and antisite defects in the product, respectively, which possibly interacted to vary thermoelectric transport properties of the product. We endeavored to balance the concentration of the defects to optimize the properties, and thus we strengthened phonon glass electron crystal characteristic of the product, resulting in the improvement in thermoelectric performance.
[en] Full text:The solid products (SnSe)1-x (TbSe)x were synthesized by the method of direct fusion of component, put for long-term evaporation, phase equilibrium studied on the basis of complex physical and chemical analyses, Tb0,01Sn0,99 and Tb0,05Sn0,95Se monocrystals obtained by the method of the directed fusion zone. A number of electro physical properties of the alloys of (SnSe)1-x (TbSe)x systems were studied before and after the radiation at the wide range of temperature (77-320K), and the impact of γ-rays on these properties examined. As known, the thermoelectric driving force (α) in the semi conductive materials is very sensitive to concentration of charge carriers and defects. That's why, as it was stated above, in order to study the impact of γ-rays on the thermoelectric driving force of the obtained samples, the dependence of α (T) at the temperature T=77-320K was measured before and after the radiation and analyze made. It was determined that the value of α at the temperature T=85K was reduced to 16 percent after the radiation in the sample with the content of x=0,05 as opposed to that with the content of SnSe and x=0,01. On the contrary, the increase was observed for 22 percent in the sample with the content x=0.01 and for 18 percent in the compound SnSe. Following the research, it was determined that the concentration of point radiation defects of acceptor-type arisen during the radiation in the alloys of TbxSn1-x systems is relatively lesser in the sample of the content x=0,05 and more resistant to radiation.
[en] Basic physical ideas and methods that are used to improve the quality of modern thermoelectric materials and to increase the thermoelectric figure-of-merit are reviewed, with special emphasis on how nanostructure affects the thermoelectric properties of materials. (reviews of topical problems)
[en] We examine the effective properties of a thermoelectric material in the vicinity of an arbitrarily shaped hole. Using complex variable methods, we establish closed-form representations of the electric and thermal fields in the matrix surrounding the hole. Specifically, we analyze the effective material parameters of a rectangular thermoelectric region containing an insulated macroscopic hole and determine that the effective electric and thermal conductivities depend strongly on the size and shape of the hole while the effective Seebeck coefficient always remains equal to that of the surrounding matrix. Perhaps most significantly, we conclude that since an insulated hole has almost the same effect on both the effective electric and thermal conductivities, its introduction does not affect the effective thermoelectric figure of merit in most thermoelectric materials. Consequently, we can conclude that, for the most part, an arbitrarily shaped hole can be inserted into a thermoelectric material without decreasing its maximum thermoelectric conversion efficiency. Our findings provide an important theoretical basis for the future design and development of thermoelectric devices.
[en] This study analyzes an interfacial edge crack in an orthotropic thermoelastic bimaterial subjected to uniform heat flux at infinity. The problem is formulated on the basis of transformed function representations of plane solutions for anisotropic thermoelastic solids. The interface stress intensity factors are obtained in terms of four proposed thermal load parameters and two dimensionless coefficient matrices. It is shown that one of the coefficient matrices depends on eight material parameters whereas the other coefficient matrix is affected by only six material parameters. The orthotropic rescaling technique is used to examine the explicit dependence of the two coefficient matrices on one orthotropic material parameter. The effects of the other material parameters on the coefficient matrices are examined numerically. The energy release rate and mode mixity for the interface crack are also obtained.
[en] Here, we introduce a simple but efficient electronic fitness function (EFF) that describes the electronic aspect of the thermoelectric performance. This EFF finds materials that overcome the inverse relationship between σ and S based on the complexity of the electronic structures regardless of specific origin (e.g., isosurface corrugation, valley degeneracy, heavy-light bands mixture, valley anisotropy or reduced dimensionality). This function is well suited for application in high throughput screening. We applied this function to 75 different thermoelectric and potential thermoelectric materials including full- and half-Heuslers, binary semiconductors, and Zintl phases. We find an efficient screening using this transport function. The EFF identifies known high-performance p- and n-type Zintl phases and half-Heuslers. In addition, we find some previously unstudied phases with superior EFF.
[en] Highlights: • Stoichiometric Bi0.5Sb1.5Te3 films are fabricated by in-situ crystallization. • The (000l) orientations and high crystallinity of these films have been realized. • Three parameters of electrical properties (μ, σ, α) are simultaneously increased. • The relationship between the electric properties and orientations are calculated. • A layer-by-layer in-situ growth model is proposed for (000l)-oriented films. The preparation of high-performance Bi2Te3-based films is vitally important for the miniaturization of Bi2Te3 thermoelectric (TE) device. Herein, a series of stoichiometric Bi0.5Sb1.5Te3 films with different preferential orientations have been fabricated through in-situ crystallization during the co-sputtering process. We discover that the preferential orientation was transformed from (015) to (1010) to (000l) orientation with increasing the substrate temperature. The (000l)-oriented films exhibit the best electrical transport properties, which the maximum electrical conductivity of 8.0×104 S·m-1 and power factor of 3.8 mW K-2·m-1 are much more than those of the bulk material. The excellent properties are attributed to the high-crystallinity, well-controlled preferential orientation, and minimized compositional deviation. A layer-by-layer in-situ growth model is proposed to understand the formation mechanism of the (000l)-oriented films. Our work demonstrates that the electrical transport performance of Bi2Te3-based films can be remarkably improved through finely controlling the crystallinity and preferential orientation under the condition of stoichiometric composition.