High-Performance Ceramics IV

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Authors: Yong Gao Yan, Xin Feng Tang, Hai Jun Liu, Ling Ling Yin, Qing Jie Zhang
Abstract: Ag1-xPbmSbTe2+m (m = 6, 10, 18; x = 0, 0.5, 0.75) compounds were prepared by melting-spark plasma sintering (SPS) process. The effects of m and x on the thermoelectric properties of the compounds were investigated. The results indicate that all samples are n-type conduction. For Ag1-xPb18SbTe20 (x = 0, 0.5, 0.75), the electrical conductivity decreases, whereas Seebeck coefficient increases, with increasing Ag concentration. For AgPbmSbTe2+m (m = 6, 10, 18), as m increases, the Seebeck coefficient slightly decreases and the electrical conductivity increases first, with a maximum at m =10, and then decreases. The thermal conductivity increases with increasing m.
Authors: Wen Bing Zhang, Li Dong Chen, Xiao Ya Li
Abstract: Polycrystalline AgPb18+xSbTe20 compounds with different Pb contents (x=1-4) were prepared by melting method and spark plasma sintering techniques. The crystal structure and chemical composition were determined by XRD and EPMA. The thermal conductivity, electrical conductivity and Seebeck coefficient were measured in the temperature range of 300-800K. The dimensionless thermoelectric figure of merit (ZT) of AgPb18+xSbTe20 (x=1-4) increases in the whole temperature range of 300-750K which is different to the pure lead telluride compound. The maximum ZT value reaches 1.03 at 800K.
Authors: Y. Gelbstein, Z. Dashevsky, R. Kreizman, Y. George, M. Gelbstein, M.P. Dariel
Abstract: Lead tin telluride based alloys are known p-type materials for thermoelectric applications, in the 50-600oC temperature range. These alloys combine desired features of mechanical and thermoelectric properties. The electronic transport properties of PbTe and Pb1-xSnxTe materials may be strongly dependent on the preparation technique. Powder metallurgy process is known to introduce defects and strains, that may alter carrier concentration. Under such non-equilibrium conditions the thermoelectric properties are instable at the operating temperature. An appropriate annealing treatment can eliminate this effect.. The present communication describes the annealing treatment applied to cold compacted and sintered Pb1-xSnxTe materials.
Authors: Wei Ren, Xue Quan Liu, Xiao Lin Wang, Hong Yi Jiang
Abstract: Polycrystalline samples of Bi2Te3 based alloys were prepared by powder metallurgy processing including a melting-grinding and a sintering procedure of compacted pellets. Two sintering procedures as hot-pressing and spark plasma sintering (SPS) were employed. The thermoelectric properties and mechanical strength were measured in all case. Thermoelectric properties for p-type (Bi0.25Sb0.75)2Te3 and n-type Bi2(Te0.2Se0.8)3 changed with sintering temperature in both sintering methods. Mechanical strength and relative density increase with sintering temperature in two sintering procedures. The results firmly suggest that both sintering procedures are promising to obtain high performance thermoelectric materials.
Authors: J.L. Cui, Y.L. Yuan, B. Hu, W. Yang
Abstract: Thermoelectric Ag-Bi-Sb-Te alloys with the general formula AgxBi0.5Sb1.5-xTe3 (x =0.05∼0.4) were prepared by spark plasma sintering and their electrical properties were examined. The alloys exhibit large electrical conductivities in the whole temperature range, which are approximate 11.0 and 3.5 times those of pseudo-binary Bi0.5Sb1.5Te3 alloy at room temperature and 558K, respectively. The highest power factor value of 1.80×10-3 (W.K-2.m-1) is obtained for the material (x = 0.1) at the temperature of 412K, being about 2.4 times that of pseudo-binary alloy Bi0.5Sb1.5Te3 at the corresponding temperature.
Authors: Yuan Deng, Chang Wei Cui, Lin Guo
Abstract: Bi porous films were prepared via a simple process which involves solvothermal or thermal treatment of Bi(NO3)3 and alumina membranes. The reducing reagent is helpful for the growth of Bi in the channels of alumina templates. However, Bi networked X-shape nanowires would form when the reaction was carried out under vacuum system. This method has been successfully applied to the synthesis of other porous metal film. The pressure, reducing reagent and starting materials play a key role in the growth of Bi films. A possible formation mechanism of Bi films and nanowires is proposed.
Authors: R. Kreizman, N. Traistman, M. Shaked, Z. Dashevsky, M.P. Dariel
Abstract: PbTe based semiconductors are characterized by a narrow energy gap and can be used for IR detectors, light emission diodes, lasers and thermoelectric devices. The objective of the present work was to study the effect of oxidation on the properties of n- and p-type PbTe samples prepared by powder metallurgy (bulk materials) and physical vapor deposition (thin films with thickness ∼1 μm). The samples were characterized by SEM, AES and XRD. The Hall effect and electrical conductivity of PbTe samples have been examined over the 80 – 300 K temperature range. The experimental results are accounted for in the framework of a model that is based on: 1- the fast diffusion of oxygen along grain boundaries (GB); 2 - oxygen absorption that generates acceptor states at GB (short time annealing) and the growth of PbTe oxides on GB with properties corresponding to wide band semiconductor (lengthy annealing); 3 - the creation of potential barriers on GB due to oxidation with a thermally activated dependence of the conductivity.
Authors: I. Dahan, M.P. Dariel
Abstract: The present communication is concerned with the interdiffusion kinetics and the interface breakdown that take place in the Nb/NbC multilayer system as the result of thermal annealing in the 400-800oC temperature range. Within this temperature range carbon is the diffusing species. Carbon diffuses from the carbide layer into the adjacent Nb layer, depleting its concentration within the carbide, causing the nucleation and subsequent growth of an intermediate Nb2C layer and decreasing the width of the original Nb layer. TEM examination of the cross-sections of the multilayer specimens provides data regarding the evolution of the microstructure and, in particular, regarding the initial nucleation stage of the newly formed Nb2C layer.
Authors: Qing Hua Wang, Jian Zhong Zhang, Li Li Zhang, Ze Shen Wang
Abstract: The conversion efficiency of heat to electricity is the basic parameter of thermoelectric element, thermoelectric unicouple and thermoelectric devices. In principle, the heat to electricity conversion efficiency of thermoelectric element has been defined as the electrical output power of the element divided by its thermal input power. Due to the heat loss by convection and radiation heat transfer the test result of the heat to electricity conversion efficiency has a large errors. The authors present a test method for heat to electricity conversion efficiency of thermoelectric unicouple. The thermal input power of thermoelectric unicouple has been divided into the electrical output power plus thermal output power out of the cold end of the unicouple. The later has been determined by a thermoelectric thermal power meter. The method avoids the difficulties to measure the input thermal power into the hot side of the unicouple, so that the convection and radiation heat lose out of the unicouple side can be ignored. Owing to Seebeck Coefficient of the thermoelectric semiconductor materials could be many times of the metals, the thermoelectric thermal power meter has high sensitivity, so that high test precision could be gained in test for conversion efficiency of thermoelectric unicouple. The paper presents some test results for heat to electricity conversion efficiency of thermoelectric unicouple, and discusses about the factors which affect the test results.
Authors: Tie Min Wang, Jian Zhong Zhang, Hong Kui Ma

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