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_...     

非简谐振动对半导体基外延石墨烯热电效应变化规律的影响

本文建立了半导体基外延石墨烯的物理模型，考虑原子的非简谐振动，研究了它的杂化势以及热电势随化学势和温度的变化规律，探讨了原子非简谐振动对热电效应的影响. 对硅基外延石墨烯热电势的研究结果表明：简谐近似下，杂化势与温度无关；只考虑到第一非简谐项，杂化势随温度升高而增大；同时考虑到第一、第二非简谐项，则杂化势随温度升高而减小. 在给定温度下，外延石墨烯的热电势随化学势的变化在化学势为 处不具左右对称性，且在化学势为 eV附近有突变；给定化学势时，外延石墨烯热电势与单层石墨烯相似，均随温度升高而非线性减小，但外延石墨烯的值大于单层石墨烯的值；与简谐近似相比，非简谐效应会减小外延石墨烯热电势的值但减小量很小. 非简谐效应对热电势的影响随温度的升高而缓慢增大，大小在0.23%~0.25%之间.     

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.     

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.     

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.     

Experimental studies on overall property of thermoelectric modules with sandwiched structures

Based on direct-current transient Harman method, an integrated characterization system of thermoelectric device’s performance is established. The overall properties of thermoelectric modules with sandwiched structures are experimentally investigated, including Seebeck coefficients, figures of merit (ZT), electrical and thermal conductivities. Experiment results reveal that ZT values of thermoelectric modules are smaller than those of commercial bismuth telluride (Bi₂Te₃) modules. In contrast, Seebeck coefficients are significantly larger than traditional thermoelectric device’s values. Meanwhile, both electrical and thermal conductivities are greater compared with literature data. Our results have proposed a feasible and economical way that can potentially increase Seebeck coefficients as to bulk Bi₂Te₃ materials without significant deterioration to the nature of Peltier effect.     

Silicon nanowires as efficient thermoelectric materials

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT-a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics, such as Bi(2)Te(3)/Sb(2)Te(3) thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm x 20 nm and 20 nm x 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT approximately 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.     

压力对稀土元素Sm填充方钴矿化合物热电性能的影响

通过高温高压方法合成出稀土元素Sm填充n型方钴矿化合物SmxCo4Sb12（0〈x〈1）,并考察了在室温下Sm填充率对热电性能的影响规律.结果表明：SmxCo4Sb12化合物表现为n型传导;电阻率和Seebeck系数随着合成压力的增加逐渐增加;晶格热导率随着Sm填充分数的增加而降低,在Sm填充量为0.5时达到最小值.室...     

Thermoelectric properties of polycrystalline (SnSe)1-x(AgSnSe2)x/2 alloys

SnSe is considered as a thermoelectric material with great potential and advantages due to the record of high thermoelectric figure of merit (ZT) of 2.6 ?at 923 ?K in single crystals. However, it is difficult to use single crystal SnSe in practice due to its poor mechanical properties and high manufacturing costs. Meanwhile, the polycrystalline SnSe also is also not suitable for applications due to its much lower thermoelectric performance compared with single crystal SnSe. Therefore, improving the thermoelectric properties of polycrystalline SnSe has become a hot research topic. In this paper, AgSnSe₂ doped into SnSe to increase the carrier density of the system and thus improve its thermoelectric properties. It is found that the addition of AgSnSe₂ can effectively improve the thermoelectric performance of polycrystalline SnSe. A peak ZT of 0.81 was obtained at 713 ?K for (SnSe)_0.95(AgSnSe₂)_0.025, which is 305% higher than that of the undoped one. This reveals that AgSnSe₂-doped SnSe alloy may become a thermoelectric material system with great application potential and significance.     

温度对石墨烯条带拉伸力学性能影响的模拟研究

利用分子动力学模拟,分析了单层石墨烯条带在热力学温度[1K,800K]范围内拉伸力学性能对条带手性,宽度及模拟温度的依赖性.结果表明,相同条件下锯齿型石墨烯条带较扶手椅型石墨烯条带具有更大的弹性模量及拉伸强度;条带宽度的增加对弹性模量有较小影响,但拉伸强度随宽度的增加有明显变化;石墨烯条带拉伸强度随温度的升高而减小,均匀变温模拟条件下拉伸强度较室温恒温模拟结果有所变化,且温度变化率是影响拉伸强度的因之一.     

石墨烯纳米带的制备方法

石墨烯纳米带(GNRs)是一种新型的一维碳纳米材料,因为它具有独特的尺寸效应、量子效应和界面效应等,使它在电子学和磁学方面有着巨大的应用前景.主要介绍了GNRs的两种制备方法:自上而下法和自下而上法.自上而下的制备方法重点描述解卷碳纳米管(CNTs)法、催化法和刻蚀法;自下而上的制备方法主要包括表面介导合成法和湿法有机合成等.     

单壁碳纳米管超声裂解制备石墨烯纳米带

将单壁碳纳米管仅通过气相氧化和超声裂解两步制备出了石墨烯纳米带,采用透射电子显微镜(TEM)、原子力显微镜(AFM)、拉曼光谱(Raman)对制备出的石墨烯纳米带进行形貌和结构分析。结果表明,此方法制备的石墨烯纳米带宽度狭窄、边缘光滑,并且相比于刚性的单壁碳纳米管具有良好的柔韧性,大约为2nm的厚度也说明了石墨烯纳米带的双层结构。在气相氧化和超声裂解的过程中,拉曼光谱中D峰与G峰的比值始终保持在0.15左右,表明在整个制备过程中,并没有引入新的缺陷。此方法相比于其他方法制备出的纳米带具有结晶度高、宽度狭窄、边缘光滑等优点。     

Influence of sintering temperature on the thermoelectric properties of Ba8Ga16Si30 clathrate treated by spark plasma sintering

A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering (SPS). X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750°C. Lattice contraction recurred when the SPS temperature was further increased in the range of 750–1000°C. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800°C. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT–T curve.     

球磨工艺调控碲化铋基材料微结构及热电性能研究

碲化铋基化合物是室温附近性能最佳的热电材料,在余热回收以及固态制冷领域具有重要的应用价值. 其主要的制备方式是球磨法,各类参数的细微变化都可能影响材料的微结构和热电性能. 球磨时间作为重要的球磨参数既能影响粉末粒径的细化,也对材料的热电性能有所调控,因此亟需逐步分析球磨时间对晶体结构、粒径尺寸及产物热电性能的影响. 本文采用恒定的球磨转速,调节不同球磨时间制备碲化铋基材料. 通过晶体结构及粉体粒径的分析发现了晶粒对球磨时间的响应. 后续热电性能测试结果表明,增加球磨时间后粒径发生变化并导致了电子、声子输运模式的协同改变. 最终,有效提升了n型与p型碲化铋的最大ZT值,分别达到了0.91和1.11. 本研究工作系统总结了球磨工艺中关键参数对碲化铋材料微结构及热电性能的影响,为粉末冶金及热电学的交叉融合及热电转换技术的商业化应用提供了实验和理论参考.     

双弯曲对称石墨烯纳米带的热电性质

运用非平衡格林函数方法,研究了双弯曲对称石墨烯纳米带结构中的电子和声子输运规律．研究结果表明：两种双弯曲对称石墨纳米带对应的ZT值可以远大于相应理想石墨纳米带对应的值;同时发现,两种双弯曲对称石墨纳米带对应ZT的最大值非常敏感地依赖于其散射区的长度和宽度的变化．     

化学镀Zn对n型Bi2Te2.4Se0.6合金热电性能的影响

为了研究化学镀Zn对n型Bi2Te2.4Se0.6材料的热电性能的影响及作用机制,采用化学镀法制备n型Zn/Bi2Te2.4Se0.6纳米粉体,并结合放电等离子烧结烧制成块体材料,n型Zn/Bi2Te2.4Se0.6热电材料的Seebeck系数(SS)提升,热导率显著降低,其中0.15％Zn/Bi2Te24Se06的热导率最低,在371 K达到最小值0.74 W/(m·K),这是由于载流子浓度的降低引起电子热导减小,以及第二相和晶界增多引起声子散射造成晶格热导降低.结果表明,0.15％Zn/Bi2Te2.4Se0.6的热电优值(ZT)有很大的提升,在421 K达到1.06.     

Thermoelectric properties of I-doped n-type Bi2Te3-based material prepared by hydrothermal and subsequent hot pressing

I-doped Bi_2Te_(3-x)I_x(x=0, 0.05, 0.1, 0.2) flower-like nanoparticles were synthesized by a hydrothermal method through a careful adjustment of the amount of ethylenediamine tetraacetic acid surfactant. The nanopowders of flower-like nanoparticles were hot-pressed into bulk pellets and the thermoelectric properties of the pellets were investigated. The results showed that I-doping decreased the electrical resistivity effectively, and the thermal conductivitives of the Bi_2Te_(3-x)I_x bulk samples was lower because of the closer atomic mass of I compared to Te.As a result, a ZT value of 1.1 was attained at 448 K for the Bi_2Te_(2.9)I_(0.1)sample.     

Fabrication and property of high-performance Ag-Pb-Sb-Te system semiconducting thermoelectric materials

High performance Ag-Pb-Sb-Te system thermoelectric bulk materials were fabricated by a combination of mechanical alloying (MA) and spark plasma sintering (SPS). Phase composition and microstructure of the resultant materials were investigated by X-ray diffraction (XRD) and scanning electron micros-copy (SEM) analysis. A special emphasis was paid to the effects of chemical composition, especially the Pb content on the thermoelectric properties of the Ag0.8Pb18 xSbTe20 samples, including electrical resistivity, Seebeck coefficient, power factor, thermal conductivity and dimensionless figure of merit. The present study reveals that the optimal composition of Ag0.8Pb18 xSbTe20 samples is Ag0.8Pb22.5SbTe20 and the maximum figure of merit (ZT) is 1.2 at 673 K.     

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.     

(Nd0.62 Li0.15)TiO3陶瓷的制备及其热电性能

采用固相反应法与无压烧结法相结合制备了ABO₃型钙钛矿(Nd_0.62Li_0.15)TiO₃晶体陶瓷材料,并对其热电性能进行了表征.高分辨率透射电镜观察显示,制备的材料具有纳米超晶格结构,导致材料表现出玻璃态热传导特征且热导率小于2W/(m·K),该玻璃态热传导源于超晶格结构形成的大量纳米域界面对声子的强烈散射.A位空位填充使材料的电子电导率得到了明显改善,但对材料的热导率影响不大.塞贝克系数因为TiO₆八面体的扭曲而受到一定的影响.在测试温度范围内,块体陶瓷在500K时得到了最高的无因次热电优值(ZT)0.019.