Improving thermoelectric properties of p-type Bi_2Te_3-based alloys by spark plasma sintering

High-performance(Bi_2Te_3)_x(Sb_1Te_3)_(1-x) bulk materials were prepared by combining fusion technique with spark plasma sintering,and their thermoelectric properties were investigated.The electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases significantly with the increase of Bi_2Te_3 content,which leads to a great improvement in the thermoelectric figure of merit ZT.The maximum ZT value reaches 1.33 at 398 K for the composition of 20%Bi_2Te_3-80%Sb_2Te_...     

Improving thermoelectric properties of p-type Bi2Te3 -based alloys by spark plasma sintering

High-performance (Bi2Te3)x(Sb2Te3)1?x bulk materials were prepared by combining fusion technique with spark plasma sintering, and their thermoelectric properties were investigated. The electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases signi ficantly with the increase of Bi2Te3 content, which leads to a great improvement in the thermoelectric figure of merit ZT. The maximum ZT value reaches 1.33 at 398 K for the composition of 20%Bi2Te3-80%Sb2Te3 with 3% (mass fraction) excess Te.     

高优值P型(BiXSb1-X)2Te3热电材料的优化制备工艺

根据影响 P型 (Bi XSb1 - X) 2 Te3半导体热电材料优值系数的主要因素和大量实验结果 ,采用高纯原料、筛选配方、慢速区熔长晶及退火等优化工艺 ,在晶锭的相当长的范围内获得了晶体结构完整、热电性能均匀、优值系数高达 3.46的半导体热电材料     

机械合金化法制备Co掺杂β-FeSi_2及性能分析

用机械合金化法成功制备了配比为Fe1-xCoxSi2(x=0.04,0.05,0.06)的N型β-FeSi2基热电材料.研究结果表明:在球料质量比为80∶ 1,球磨速度为400 r/min的条件下,球磨20 h的粉体发生完全合金化,生成β-FeSi2,α-Fe2Si5和ε-FeSi的合金相;经过1 373 K退火2 h,再结合1 073 K退火2 h的热处理后,可完全获得晶粒细小的N型块状β-FeSi2;随着测量温度的升高,Fe1-xCoxSi2试样的Seebeck系数α和电导率σ增大,热导率κ降低,无量纲热电优值ZT随温度升高而明显增大;随着掺杂量的增加,材料的电导率σ增大,热导率κ降低,σ/κ比值得到提高,但Seebeck系数α降低;当T=695 K,掺杂量x=0.04时,Seebeck系数α的最大绝对值为227 μV/K;具有最佳热电优值的材料为Fe0.95Co0.05Si2.     

电化学组装一维纳米线阵列温差电材料

低维温差电材料具有比块状温差电材料更高的优值,因而研制具有纳米线阵列结构的温差电材料对于提高材料的温差电转换效率具有重要意义.以具有纳米孔阵列结构的氧化铝多孔模板为阴极,在含有Bi 3、HTeO2 1的酸性溶液中,采用直流电沉积技术,通过在氧化铝多孔模板的纳米级微孔中沉积铋和碲,实现了一维纳米线阵列铋碲温差电材料的电化学组装.环境扫描电子显微镜(ESEM)和透射电子显微镜(TEM)的分折表明,电化学组装出的铋碲纳米线分布均匀,形状规则.铋碲纳米线的组成可方便地通过调整电沉积电位加以控制.     

半导体材料优值系数对热电堆发电循环效率的影响

从半导体能量微分方程出发,推导出半导体热电发电循环效率与材料优值系数ZT之间的关系,指出目前半导体热电发电循环效率较低的原因及提高途径,为今后提高半导体热电发电循环的性能奠定了基础。     

Ag,Er,Cu双掺杂对Ca3Co2O6热电性能的影响

采用溶胶 凝胶法和常压烧结技术, 制备一系列钴基氧化物热电材料Ca₃Co₂O₆和Ca_2.85M_0.15Co_2-yCu_yO₆(M=Ag,Er; y=0,0.1,0.2), 并通过X射线衍射(XRD)和扫描电子显微镜(SEM)考察样品的物相组成和微观形貌, 在300~1 000 K测定样品的电导率和Seebeck系数, 分析掺杂不同元素对复合物热电性能的影响. 结果表明: 制备的所有材料均为单一物相, 结构致密; 不同双掺杂元素对材料的热电性能均有提升作用; 当Ag⁺和Cu²⁺的掺杂量分别为0.15,0.2时, 可获得最优的热电性能, Ca_2.85Ag_0.15Co_1.8Cu_0.2O₆在965 K时的功率因子为71 μW/(K₂·m).     

Enhanced thermoelectric performance of rough silicon nanowires

Approximately 90 per cent of the world's power is generated by heat engines that use fossil fuel combustion as a heat source and typically operate at 30-40 per cent efficiency, such that roughly 15 terawatts of heat is lost to the environment. Thermoelectric modules could potentially convert part of this low-grade waste heat to electricity. Their efficiency depends on the thermoelectric figure of merit ZT of their material components, which is a function of the Seebeck coefficient, electrical resistivity, thermal conductivity and absolute temperature. Over the past five decades it has been challenging to increase ZT > 1, since the parameters of ZT are generally interdependent. While nanostructured thermoelectric materials can increase ZT > 1 (refs 2-4), the materials (Bi, Te, Pb, Sb, and Ag) and processes used are not often easy to scale to practically useful dimensions. Here we report the electrochemical synthesis of large-area, wafer-scale arrays of rough Si nanowires that are 20-300 nm in diameter. These nanowires have Seebeck coefficient and electrical resistivity values that are the same as doped bulk Si, but those with diameters of about 50 nm exhibit 100-fold reduction in thermal conductivity, yielding ZT = 0.6 at room temperature. For such nanowires, the lattice contribution to thermal conductivity approaches the amorphous limit for Si, which cannot be explained by current theories. Although bulk Si is a poor thermoelectric material, by greatly reducing thermal conductivity without much affecting the Seebeck coefficient and electrical resistivity, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials.     

半导体制冷技术的研究现状及发展方向

半导体制冷技术是一门以热电制冷材料为基础的新兴制冷技术.通过阅读大量文献,从热电材料、结构设计、冷热端散热方式3个方面对半导体制冷技术近年来的研究热点和成就进行了总结和论述,并指出了半导体制冷技术的发展方向.热电材料决定了优值系数Z,可以从根本上提高材料的制冷性能,但研究难度较大,发展缓慢;优化结构设计可以有效地提高制冷单元的实际性能系数,重点在于优化尺寸因子G和热电阻,缺点是实际加工工艺复杂;减小热电偶冷热端的温差有利于提高制冷量,可以大幅提高制冷系数,有效的散热方式是提高半导体制冷效率的重要因素.     

一种MEMS热电制冷器的设计

研究一种基于MEMS工艺的微型热电制冷器.采用薄膜热电材料减小器件的尺寸,采用微机械加工工艺形成的硅杯结构降低衬底的热泄漏.器件在材料和工艺上都与微电子工艺兼容,易于与电子器件集成.分别讨论了热电臂长度、厚度及绝缘膜厚度等结构参数对器件最大制冷温差、制冷系数、制冷功率等性能的影响,得出最优的设计参数.分析中考虑了绝缘层热泄漏,制冷区的热对流和热辐射,以及接触电阻等非理想因素.分析结果表明,器件工作时达到的最大温差为40 K;冷端温度为290 K时,制冷功率为3 mW.     

Na_xCo_2O_4热电材料的研究进展

介绍了NaxCo2O4氧化物热电材料的基本结构和热电性能,论述了NaxCo2O4热电材料的研究进展,并对NaxCo2O4材料的Na位掺杂(掺入K,Sr,Y,Nd,Sm,Yb,Ca,Ag)和Co位掺杂(掺入Ti,Rh,Pd,Pb,Mn,Ru)进行了评述·不同元素对Na位和Co位的掺杂效果的影响是不同的,但可以看出NaxCo2O4热电材料的掺杂研究有着非常好的研究价值和应用前景·     

成型压力和掺杂对Na1.4Co2O4基材料性能的影响

采用溶胶-凝胶法制备了Na位掺杂Sr和Li(掺杂量分别为0.1,0.2,0.3和0.4)的Nal.4Co2O4基热电材料,研究了成型压力和掺杂对Nal.4Co2O4基材料电导率、Seebeck系数和功率因子等热电性能的影响.采用XRD分析了NaxCo2O4基热电材料的相组成.研究结果表明:掺杂Sr和Li制备的Nal.4...     

Thermoelectric properties of p-type Bi-Sb-Te compositionally graded thermoelectric materials with different barriers

In order to find more suitable materials as barriers and to improve the thermoelectric properties, p-type (Bi_l-xSb_x)₂ Te₃ (x=0.85, 0.9) two segments compositionally graded thermoelectric materials (CGTM) with different barriers were fabricated by conventional hot pressure method. Metals Fe, Co, Cu and Al were used as barriers between two segments. The effects of different barriers on thermoelectric properties of CGTM were investigated. The results show that metal Fe is more stable and suitable as the barrier.     

高温高压对Bi_(0.45)Sb_(1.55)Te_3热电性能的调控

采用高温高压法在30min内实现从元素粉末(Bi,Sb,Te)到块体纯相Bi_(0.45)Sb_(1.55)Te_3的快速合成,并利用X射线衍射、场发射扫描电子显微镜及高分辨透射电子显微镜表征样品的相成分和微结构,测试其在室温下的电输运性能.结果表明:高温高压法是一种简单、快速合成块体热电材料的途径;Bi_(0.45)Sb_(1.55)Te_3样品由结晶性良好的典型层状晶体构成;电阻率随合成压力的升高而增加;合成压力为2GPa的样品获得最大功率因子为10.85μW/(cm·K~2).     

热电氧化物(Ca_3Co_2O_6)_(1-x)(Ca_3Co_4O_9)_x的制备和表征

热电氧化物Ca3Co2O6和Ca3Co4O9是Ca-Co-O体系中两个确定的态,其热电性质显著不同.我们采用“快速加热法”制备了(Ca3Co2O6)1-x(Ca3Co4O9)x(x=0,0.2,0.4,0.6,0.8,1),并利用XRD、SEM等实验方法分析表征样品,系统研究了热电氧化物从Ca3Co2O6到Ca3Co4O9的转化过程.从SEM图中可知Ca3Co2O6为无规取向棒状结构,Ca3Co4O9为法向取向与表面近似垂直的片状结构,XRD结果显示x=0.4之前的样品Ca3Co2O6和Ca3Co4O9两相衍射峰并存,x=0.6以后的样品是Ca3Co4O9单相.     

Effect of high pressure sintering and annealing on microstructure and thermoelectric properties of nanocrystalline Bi2Te2.7Se0.3 doped with Gd

Bi2Te2.7Se0.3of high performance doped with Gd bulk materials was prepared by a high pressure(6.0 GPa) sintering(HPS) method at 593 K,633 K, 673 K and 693 K. The sample was then annealed for 36 h in a vacuum at 633 K. The phase composition, crystal structure and morphology of the sample were analyzed by X-ray diffraction and scanning electron microscopy. The electric conductivity, Seebeck coefficient, and thermal conductivity aspects of the sample were measured from 298 K to 473 K. The results show that high pressure sintering and the doping with Gd has a great effect on the crystal structure and the thermoelectric properties of the samples. The samples are consisted of nanoparticles before and after annealing, and these nanostructures have good stability at high temperature. HPS together with annealing can improve the TE properties of the sample by decreasing the thermal conductivity of the sample with nanostructures. The maximum ZT value of 0.74 was obtained at 423 K for the sample, which was sintered at 673 K and then annealed at 633 K for 36 h. Compared with the zone melting sample, it was increased by 85% at423 K. Hence the temperature of the maximum of figure of merit was increased. The results can be applied to the field of thermoelectric power generation materials.     

氧化石墨增强高分子材料热电性能的初步研究

分别以尼龙6和聚吡咯为基体，氧化石墨为填料，通过原位聚合反应制备了尼龙6-氧化石墨及聚吡咯-氧化石墨复合材料。两种复合材料的热电性能测试数据表明：氧化石墨在尼龙6基体中被同步还原为导电填料，尼龙6从绝缘体转变为半导体，热电性能大大增强，最大热电优值为9.45×10^-6；氧化石墨在吡咯聚合过程中扮演着模板的角色，促成聚吡咯分子链有序排列及堆积，热电性能增强，且复合材料的电导率和Seebeck系数的最大值分别达到6056S/m和9.85μV/K^-1，对应的热电优值为6.89×10^-4。     

Thin-film thermoelectric devices with high room-temperature figures of merit

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.     

热电材料的研究进展

简要介绍了热电效应、热电材料性能评价方法,给出了评价热电材料的必要条件及改善品质因子的几种途径,系统阐述了热电材料的研究发展过程和近几年的最新研究动向.     

具有不同扩散势垒的p型(Bi1-0.85Sb0.85)和PbTe二元梯度热电材料的研制

在分析了热电材料的发展背景和研究理论的基础上,采用热压法制备出单体和双层具有不同扩散势垒的（Ｂｉ１－０．８５Ｓｂ０．８５）２Ｔｅ３与ＰｂＴｅ体系二元梯度热电材料,金属,Ｆｅ、Ｎｉ和Ｍｇ被用作层间扩散势垒材料,测定了它们的热电性能,分析了它们的物质组成和各层内和层间的成分分布,确定出较好的扩散势垒材料为金属铁和钴。