Molecularly Protected Bismuth Telluride Nanoparticles: Microemulsion Synthesis and Thermoelectric Transport Properties
Molecularly Protected Bismuth Telluride Nanoparticles: Microemulsion Synthesis and Thermoelectric Transport Properties
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DOI：
10.1002/adma.200600495
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发表时间：
2006-11
影响因子：
29.4
通讯作者：
A. Purkayastha;S. Kim;D. Gandhi;P. G. Ganesan;T. Borca-Tasciuc;G. Ramanath
中科院分区：
文献类型：
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作者：
A. Purkayastha;S. Kim;D. Gandhi;P. G. Ganesan;T. Borca-Tasciuc;G. Ramanath
热电器件的效率是材料无量纲品质因数 ZT [1] 的函数，其中 T 是绝对温度，Z= σα2/κ； α= 热电势或塞贝克系数，σ= 电导率，κ= 热导率； Z 的分子称为功率因数。用于冷却和发电的最先进的热电材料具有 ZT∼1，而 ZT∼4 是超越竞争技术所必需的。[2] ZT 的阶乘增强可以通过在一维、二维或三维中引入纳米级几何限制来获得，例如，分别采用纳米层量子阱超晶格、纳米线和量子点超晶格。[3-6] 界面和纳米结构边界处热载流子散射的增加被认为会降低 κ，而费米能级附近载流子密度的变化提供了增加 σ 和 α 的可能性。[3,6,7-11]在 Bi2Te3/Sb2Te3 纳米层超晶格中观察到 κ，[3] 导致 ZT 增加约两倍（报道的最高 ZT∼2.3）。在 PbSeTe/PbTe 量子点超晶格中观察到主要由于 κ 减少而导致的 ZT 增加更大（与体积值相比大约五倍）。 [6]然而，ZT 的大小仅为约。 1.6 因为 PbSeTe/PbTe 块体的 ZT 低于 Bi2Te3/Sb2Te3。通过引入 3D 限制（即产生纳米颗粒）来降低块体形式固有高 ZT 的材料（例如碲化铋）的热导率，预计会产生更高的 ZT 值。这种方法还可以通过定制纳米颗粒的尺寸和形状来调节量子效应，以促进增加 ZT 的额外机制。事实上，在组织良好的 Si/Ge 纳米粒子阵列中，预计功率因数会因这种效应而增加。 [11]因此，碲化铋纳米颗粒的合成和组装对于开发用于热电冷却和发电的更高效率的设备具有重要意义。碲化铋纳米粒子的直径约为。 100 nm 已通过多种途径合成。例子包括在密封容器中在高于 600°C 的温度下熔化组成元素；[12] 通过三（二甲胺）铋和双（三甲基硅基）碲化物在己烷中反应进行低温（约 30°C）沉淀，然后在 160°C 下退火；[13] 铋和碲氧化物在水中共沉淀，然后进行氢还原；[14] 或通过还原有机金属复合体。[15]更小的（例如，20-40 nm）纳米结构可以通过溶剂热技术[16, 17]使用前体在溶剂中实现，例如N,N-二甲基甲酰胺或水，在100-180℃的还原环境下。然而，这些反应中的高温或长反应时间不利于获得小于 20 nm 的纳米结构，而在这种尺寸范围内，量子限制效应预计会很显着。 [18]最近的一份报告 [19] 展示了一种有吸引力的室温微乳液技术的使用，该技术使用水/油混合物与表面活性剂模板，从高氯酸氧化铋和双（三甲基甲硅烷基）碲化物生产直径 5 nm 的碲化铋纳米颗粒。该技术可以通过调节水/表面活性剂的比例来定制水纳米滴的形状和尺寸，从而控制纳米颗粒的形状和尺寸。然而，缺少封端剂使得纳米颗粒容易团聚，并且可能限制纳米颗粒转移到其他介质或将它们组装在基材上的能力。此外 …
The efficiency of thermoelectric devices is a function of the non-dimensional figure of merit ZT [1] of the material, where T is the absolute temperature and Z= σα2/κ; α= thermoelectric power or the Seebeck coefficient, σ= electrical conductivity, κ= thermal conductivity; the numerator of Z is referred to as the power factor. State-of-the-art thermoelectric materials usable for cooling and power generation have a ZT∼ 1, whereas a ZT∼ 4 is necessary to surpass competing technologies.[2] Factorial enhancements in ZT may be obtained by introducing nanoscopic geometrical confinement in one, two, or three dimensions, for example, nanolayered quantum-well superlattices, nanowires, and quantum-dot superlattices, respectively.[3–6] Increased scattering of heat carriers at interfaces and nanostructure boundaries are thought to decrease κ, while changes in charge carrier density near the Fermi level offers possibilities for increasing σ and α.[3, 6, 7–11] Decreases in κ have been observed across Bi2Te3/Sb2Te3 nanolayer superlattices,[3] giving rise to approximately twofold increase of ZT (highest reported ZT∼ 2.3). Even larger ZT increases (approximately fivefold compared with the bulk value) due mainly to the reduction of κ have been observed in PbSeTe/PbTe quantum-dot superlattices.[6] However, the magnitude of ZT is only ca. 1.6 since PbSeTe/PbTe bulk has a lower ZT than Bi2Te3/Sb2Te3. Lowering the thermal conductivity of materials with an inherently high ZT in the bulk form (eg, bismuth telluride), by introducing 3D confinement, that is, producing nanoparticles, is expected to yield higher ZT values. This approach could also allow the tuning of quantum effects by tailoring the nanoparticle size and shape, to facilitate additional mechanisms for increasing ZT. Indeed, power-factor increases have been predicted to arise from such effects in wellorganized Si/Ge nanoparticle arrays.[11] Hence, synthesis and assembly of nanoparticles of bismuth telluride is of interest to enable the development of higher efficiency devices for thermoelectric cooling and power generation. Bismuth telluride nanoparticles with diameters of ca. 100 nm have been synthesized by several routes. Examples include melting the constituent elements in sealed vessels above 600 C;[12] low-temperature (ca. 30 C) precipitation by reacting tris (dimethylamine) bismuthine and bis (trimethylsilyl) telluride in hexane, and subsequent annealing at 160 C;[13] co-precipitation of bismuth and tellurium oxides in water followed by hydrogen reduction;[14] or through reduction of organometallic complexes.[15] Smaller (eg, 20–40 nm) nanostructures can be realized by solvothermal techniques [16, 17] using precursors in solvents such as N, N-dimethylformamide or water at 100–180 C in reducing ambients. The high temperatures or long reaction times in these reactions, however, are not conducive for obtaining nanostructures smaller than 20 nm, which is the size regime where quantumconfinement effects are expected to be significant.[18] A recent report [19] has demonstrated the use of an attractive room-temperature microemulsion technique that uses water/oil mixtures with surfactant templates to produce 5 nm diameter bismuth telluride nanoparticles from bismuth oxide perchlorate and bis (trimethylsilyl) telluride. This technique allows control over nanoparticle shape and size by means of tailoring the shape and size of the water nanodroplet by adjusting the water/surfactant ratio. However, the absence of capping agents makes the nanoparticles susceptible to agglomeration, and could limit the ability to transfer the nanoparticles to other media or assemble them on substrates. Furthermore …