N-type doping and thermoelectric properties of co-sublimed cesium-carbonate-doped fullerene

Organic semiconductors exhibit a large Seebeck coefficient and a poor thermal conductivity allowing them to become strong candidates for thermoelectric applications. These materials have been widely used in organic electronics with the fabrication of organic light-emitting diodes, organic solar cells, and transistors. However, few studies have reported on thermoelectric properties of organic materials even though they offer specific advantages such as cost-effectiveness and flexibility. In this article, we discuss the fabrication and characterization of fullerene C60 doped with cesium carbonate (Cs₂CO₃). The evolution of the morphology, electrical conductivity, and Seebeck coefficient was analyzed as a function of the dopant concentration. An optimal power factor of 28.8 μWm^?1 K^?2 was obtained at room temperature for a molar ratio of 15.2 %. Thus far, this power factor value constitutes the best thermoelectric performance achieved with N-type organic materials.     

两段式结构赝三元材料热电模块的研究

在实验研究单段式结构赝三元材料的热电模块基础上,利用现有半导体致冷器生产工艺,依据热电材料的温度特性和冷热端工作温度,采用不同电阻率的赝三元材料,设计制作了两段式结构的热电模块．研究表明,当冷、热端工作温差为80K时,其输出功率和发电效率均比单段式结构的热电模块提高80％左右．     

Bonding and interfacial reaction between Ni foil and n-type PbTe thermoelectric materials for thermoelectric module applications

Integration of next generation thermoelectric materials in thermoelectric modules requires a novel or alternative approach for mating the brittle semiconducting thermoelectric materials and the ductile metal interconnects. In this study, pure Ni foil was directly bonded to PbTe-based thermoelectric materials using a rapid hot-press. The materials were sintered at 600 and 650 °C, under a pressure of 40 MPa and for various holding times. The resulting interfacial microstructures of the Ni/PbTe joints were investigated. Additionally, the distributions of elements and the phases formed at the Ni/PbTe interface were analyzed. The β₂ phase (Ni_3±x Te₂, 38.8–41 at.% Te) was identified at the Ni/PbTe joints bonded at both 600 and 650 °C. A ternary phase with approximate composition Ni₅Pb₂Te₃ was found at the Ni/PbTe joints bonded at 650 °C. Additionally, the PbTe(Ni) phase was observed along the Ni grain boundaries for both bonding temperatures. Thermodynamics calculation results indicate that only the β₂ phase can be formed at the Ni/PbTe interface at 900 K among the binary nickel tellurides.     

便携式热电制冷器制冷性能优化的试验分析

设计、组装一台便携式热电制冷器并对其性能进行试验研究,结果显示,200 mL的水在33 min内降温17.0℃,折合制冷量7.3 W,制冷器容器的高度方向上存在较大温差,且水温降低后密度增大而下沉,使水的自然对流换热过程受到抑制,这2个因素的综合作用使制冷片冷热端温差增大,制冷量减小,工况恶化。为优化该制冷器的制冷性能,在制冷片冷端增设重力式热管(充注R134a)并进行试验研究,结果表明,1 L的水在75 min内温度降低12℃,折合制冷量9.3 W,比优化前增大了27.4%。表明重力式热管的加入能够改善制冷器内水的对流换热情况,增大换热面积,减小竖直方向上的传热温差。     

水冷式半导体冰箱制冷性能的研究

研究了水冷式散热方法对半导体冰箱制冷性能的提高.以常用的半导体小冰箱为实例,分别测试了在风冷、循环水和恒温水条件下小冰箱的制冷性能.结果表明,水冷制冷效果明显优于传统风冷式,且其制冷性能与冷却水的温度有关.水温越低,半导体制冷器的制冷效率越高,制冷温度越低.当冷却水温度为171 ℃时,水冷半导体小冰箱很快达到冷冻.建立了水冷式半导体冰箱的制冷模型,计算分析了在不同恒定冷却水温度下半导体制冷器冷端温度随时间的变化关系,并将理论结果与实验测量结果进行了拟合分析,发现理论模型与实验测量结果一致.研究结果为水冷式半导体冰箱制冷性能的提高提供了实验和理论依据.     

Geometrical design of thermoelectric generators based on topology optimization

This paper discusses an application of the topology optimization method for the design of thermoelectric generators. The proposed methodology provides the optimized geometry in accordance with various arbitrary conditions such as the types of materials, the volume of materials, and the temperature and shape of the installation position. By considering the coupled equations of state for the thermoelectric problem, we introduce an analytical model subject to these equations, which mimics the closed circuit composed of thermoelectric materials, electrodes, and a resistor. The total electric power applied to the resistor and the conversion efficiency are formulated as objective functions to be optimized. The proposed optimization method for thermoelectric generators is implemented as a geometrical optimization method using the solid isotropic material with penalization method used in topology optimizations. Simple relationships are formulated between the density function of the solid isotropic material with penalization method and the physical properties of the thermoelectric material. A sensitivity analysis for the objective functions is formulated with respect to the density function and the adjoint equations required for calculating it. Depending on the sensitivity, the density function is updated using the method of moving asymptotes. Finally, numerical examples are provided to demonstrate the validity of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.     

NaCo2O4及其Na位掺杂热电材料的制备研究

NaCo2O4是氧化物热电材料的典型代表,也是目前人们研究较多的一种热电材料,本文采用固相反应法和溶胶-凝胶法对NaCo2O4以及Na位掺杂K、Ca、Sr、Ce试样进行制备研究.选择合适的工艺参数,采用快速升温法,可获得纯度较高(大于94%)的NaCo2O4,并使掺杂元素K、Ca、Sr进入到NaCo2O4晶格中,而Ce由于原子半径太大,难以掺杂入NaCo2O4晶格.实验结果表明采用柠檬酸溶胶-凝胶法比固相反应法制备的试样晶粒尺寸更细小,增加声子散射,使晶格热导率降低,由此提高材料的热电优值,进一步改善材料的热电性能.     

Effects of cation doping on thermoelectric properties of Bi2S3 materials

Bi₂S₃ polycrystals doped with Al, Mn, Ag, and In were fabricated by vacuum melting and plasma activated sintering process, and the phase, microstructure, electrical, and thermal properties were investigated. The electrical conductivity is enhanced via Al and Ag doping. Compared with the Ag dopant, a higher electrical conductivity is achieved in the Al-doped sample, resulting in a peak power factor value of 1.96 μW/cmK² at 423 K. Meanwhile, the thermal conductivity of Bi_1.99Al_0.01S₃ sample is very low in the Bi₂S₃ system due to the high-density defects, and is only 0.39 Wm^?1 K^?1 at 740 K. By combining a power factor and a low thermal conductivity, a peak ZT value of 0.29 at 740 K is achieved in the Bi_1.99Al_0.01S₃ sample, being about two times larger than that of pristine Bi₂S₃.

     

CuAgSe nanocrystals: colloidal synthesis,characterization and their thermoelectric performance

CuAgSe is a promising thermoelectric (TE) material for its superior carrier mobility and ultralow lattice thermal conductivity. Herein, we present a scalable colloidal method to prepare monodisperse CuAgSe nanocrystals with high yield. The collected powder sample was washed by a sulfur-free reagent of NaNH₂ to remove the surface organic ligands (CuAgSe-W) and then annealed (CuAgSe-W-A). Both kinds of ligand-free samples were then hot pressed into dense pellets to measure the TE property. The results revealed that the crystal structure of both samples changed from low-temperature β-phase to high-temperature α-phase at around 465 K. Sample CuAgSe-W shows interesting temperature-dependent transition from N-type to P-type, which could be potentially used as thermal control transistor. Sample CuAgSe-W-A does not display this transition state but it exhibits potential for intermediate temperature TE applications with a figure-of-merit zT reaching 0.68 at 566 K.     

一种新型便携式制冷保温容器的试验研究

研制一种新型便携式制冷保温容器制冷系统，主要用于保存血液。确定半导体制冷核心部件的参数，如半导体制冷片的选择、容器内部结构及系统的匹配。通过性能试验进行优化，对影响半导体制冷的因素进行讨论。实验结果表明，将半导体制冷应用于保温容器是可行的，而且是有利的。该研究结果对半导体制冷技术在小型制冷保温容器中的进一步研究和应用具有一定的指导意义。     

Effect of tellurium doping on the thermoelectric properties of CoSb3

Polycrystalline Te-doped CoSb₃ materials with various Te content have been obtained. The scanning microscope with the electron-probe microanalysis apparatus (EPMA) and XRD technique were used to investigate microstructures and to carry out the phase analysis. The Rietveld refinement method was used for refining structure parameters and for examining tellurium distribution in the CoSb₃ structure. Thermoelectric properties have been investigated by means of the Seebeck coefficient, thermal, and electrical conductivity measurements. Optimal contents of Te for maximum figure of merit ZT have been determined.     

Zr~(4+)掺杂对LiFePO_4电化学性能及微观缺陷的影响

通过高温固相法合成了掺杂Zr4+的正极材料Li1-xZrxFePO4(x=0、0.005、0.01、0.02、0.03、0.04)。采用X射线衍射(XRD)、扫描电镜(SEM)、恒流充放电、交流阻抗(ACI)和正电子湮没寿命谱(PALS)等分析测试技术对掺杂材料的晶体结构、形貌、电化学性能和微观缺陷进行研究。结果表明,在整个掺杂范围内,所有样品都具有单一的橄榄石结构,且样品表面形貌和颗粒尺寸的变化较小;掺杂系列样品中,Li0.99Zr0.01FePO4具有最好的电化学性能,在0.1C充放电倍率下,首次放电比容量达到141.6mAh/g,高于未掺杂的LiFePO4的容量107.4mAh/g,经30次循环后Li0.99Zr0.01FePO4的容量保持率为75.8%。交流阻抗谱研究表明,掺杂Zr4+使锂离子脱嵌过程中电荷转移反应的阻抗明显减小;正电子湮没寿命谱研究表明掺杂Zr4+可以在样品晶格内部产生空位缺陷,使正电子湮没寿命增加,从而提高材料电导率。     

Strain effects on thermoelectric properties of two-dimensional materials

Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride (hBN), phosphorene, transition metal dichalcogenides (e.g., MoS₂, WS₂, etc.), metal oxides (e.g., MoO₃) have attracted much attention recently due to their extraordinary structural, mechanical and physical properties. In particular, 2D materials have shown great potential for thermal management and thermoelectric energy generation due to their fascinating electrical and thermal transport properties, which can lead to a significantly large figure-of-merit. Also due to their large stretchability, 2D materials are promising for using strain engineering to tune and modulate their electronic and thermal properties, which can further enhance their figure-of-merit. In this article, we give a review on the recent advances in the study of strain-engineering on the thermoelectric properties of 2D materials. We first review some important aspects in thermoelectric effects, such as Peltier effect, Seebeck effect, the coefficient of performance and figure-of-merit (ZT) and discuss why 2D materials are ideal candidates for thermal management and thermoelectric applications. We then briefly discuss the strain (stress) generation in 2D materials and their structure integrity under strain (stress). Next, we discuss how strain affects the electronic properties of 2D materials, followed by the discussion on the effects of strain on the thermal properties of 2D materials. Subsequently, we discuss the strain effects on two important thermoelectric properties, Seebeck coefficient and figure-of-merit ZT. Finally, we present our conclusions and future perspective.     

Improvement in the thermoelectric properties of CaMnO3 perovskites by W doping

Perovskite manganites CaMn_1?y W _y O₃ (0 ≤ y ≤ 0.05) were synthesized using solid-state reaction technique. The influence of W doping on the structure, charge carrier transports and phonon scattering of CaMnO₃ was investigated. Doping was found to increase the carrier concentration, leading to enhanced electrical conductivity and decreased Seebeck coefficient. In addition, it decreased the thermal conductivity of CaMnO₃, which was believed to associate with decreased phonon mean path and doping-induced MnO₆ octahedral distortion, as evidenced by the increased orthorhombicity. A twofold increase of figure of merit (ZT) of 0.15 at 973 K was observed in CaMn_0.99W_0.01O₃, compared with the undoped CaMnO₃.     

PZT掺杂改性研究进展及其机理探究

PZT作为典型的钙钛矿结构,该结构为掺杂改性提供了较大的自由度。介绍了PZT压电材料掺杂改性的研究现状,简明扼要的分析了等价掺杂、高价掺杂、低价掺杂以及复合掺杂对压电材料各项性能的影响。并从掺杂离子对晶体结构和电畴结构影响两方面探讨了PZT掺杂改性的机理,进而为复合掺杂改性提供理论基础。     

Mg2Si与掺杂系列的电子结构与热电性能研究

用离散变分密度泛函分子轨道方法(DFT-DVM)计算了Mg2Si与掺Sb,Te和Ag系列,讨论了电子结构与热电性能之间的关系.掺杂使得离子键和共价键强度降低,在费米能级附近的能隙变小,从而提高材料电导率,降低材料热导率,优化了材料的热电性能.以上结论与实验结果一致.     

Preparation, characterization and photocatalytic performances of materials based on CS2-modified titanate nanotubes

CS₂-modified titanate nanotubes (CS₂/TiO₂-NTs) are fabricated by reaction of CS₂ and Ti-O^?Na⁺ species on titanate nanotubes. Pb²⁺ ions are coated on the modified nanotubes by ion exchange (Pb/CS₂/TiO₂-NTs). The products are characterized by means of nitrogen adsorption-desorption isotherms at 77 K (BET method), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), atomic absorption spectrometry (AAS), and diffuse reflectance spectroscopy (DRS). The photocatalytic performances of the products are evaluated by monitoring their catalytic activities for degradation of methyl orange under UV light irradiation. The effects of calcination temperature and atmosphere on the photocatalytic performance are investigated. The results reveal that the photocatalytic activities of CS₂/TiO₂-NTs and Pb/CS₂/TiO₂-NTs are far higher than that of primary nanotubes, and the optimum calcination temperature is 500 °C under N₂ atmosphere. It is also discovered that physically adsorbed Pb²⁺ ions affect the photocatalytic activity of Pb/CS₂/TiO₂-NTs obviously. The photocatalytic activity of washed Pb/CS₂/TiO₂-NTs is higher than that of the unwashed one under the same thermal treatment and reaction conditions.     

The effect of Cu-sites doping on electrical properties of La2CuO4 as thermoelectric material

The electrical conductivity and thermoelectric power for solid solutions of La₂Cu_0.9M_0.1O₄ (M = Mn, Fe, Co and Ni) prepared by polymeric precursor synthesis were measured between 300 and 1173 K to test its suitability as a thermoelectric material. Fe-, Mn-and Ni-doped compositions exhibited a metal-semiconductor transition with decreasing temperature, whereas Co doping showed a semiconducting behaviour in the entire temperature range of measurement. With Cu-sites doping in La₂CuO₄, power factors were not enhanced.     

Experimental investigation on two-stage thermoelectric cooling system adopted in isoelectric focusing

Performance of temperature control is crucial to the operation of isoelectric focusing equipment (IEF). In this paper, two-stage thermoelectric cooling module (TEM) is proposed to be adopted in IEF to realize prompt and precise temperature control as well as low focusing temperature (T_f). Three different prototypes including HP + baffle, AL + baffle and HP + fin are developed to obtain optimal design. Experimental setups of these prototypes are built up to test their performance. Temperature distribution on cooling plate, COP and air temperature in bottom chamber with respect to different T_fs are adopted as performance indices to evaluate performance of these prototypes. Experimental results show that aluminum plate with heat pipes, used as cooling plate, can improve its temperature uniformity. Moreover, fin-type heat sink with baffle can effectively dissipate heat on the hot side of TEM with little impact on the other parts of IEF. The T_f of HP + baffle can be kept at 10 °C. And its COP can reach 2.0 under general working condition.