Colloidal Nanocrystal Routes to Inorganic Nanocomposite Thermoelectric Materials

在材料研究部固体和材料化学项目的支持下，本项目合成和表征了先进的纳米复合热电材料。热电材料直接将温差转换为电压差，反之亦然。这种现象使得固态热电发电机和冷却器的创造成为可能，在解决能源格局和气候变化方面发挥着有希望的作用。热电器件最有前途的应用之一是将废热（例如汽车尾气）转化为电能。热电冷却器也很有前途，因为这些设备不使用制冷剂，而制冷剂通常是强效温室气体。作为这项活动的一部分，首席研究员正在为内燃机本科课程创建热电实验室模块。该实验室将热电装置集成到发动机的排气系统中，从而能够研究废热转化为电能。发动机还配备了一个测功仪，用于表征其机械功率。因此，学生能够测量热电装置产生的电功率，因为它们与发动机的主要变量有关：速度和扭矩。 本项目的目标是通过结合三种不同的机制来提高纳米复合材料的性能，从而推进热电材料领域。首先，这些复合材料的微观结构由嵌入基体中的纳米颗粒组成。这种形态促进强声子散射和有利的热导率降低。第二，量子限制纳米晶体被用于纳米颗粒夹杂物。这种限制导致电子态密度的尖峰，这导致大的热电功率因子。最后，带收敛被用来创建一个大的有效带简并，这进一步促进大的热电功率因数。胶体纳米晶体和金属硫族化物簇前体被组合为模块构建块，以创建纳米复合材料。纳米复合材料的局部原子和电子结构的特征在于使用像差校正的扫描透射电子显微镜配备了高分辨率电子能量损失光谱仪。一套完整的热电性能测量（即塞贝克系数，电导率和热导率）正在进行的纳米复合材料在很宽的温度范围内。总的来说，该项目结合了新型纳米复合材料的形成、原子材料的表征和热电测量套件，能够有针对性地发现热电设计规则，以提高性能。

Non-technical AbstractWith the support of the Solid State and Materials Chemistry program in the Division of Materials Research, this project synthesizes and characterizes advanced nanocomposite thermoelectric materials. Thermoelectric materials directly convert temperature differences into voltage differences and vice versa. This phenomenon enables the creation of solid-state thermoelectric power generators and coolers that can play a promising role in addressing the energy landscape and climate change. One of the most promising applications of thermoelectric devices is the conversion of waste heat (e.g. automotive exhaust) into electricity. Thermoelectric coolers are also promising because these devices do not use refrigerants, which are generally potent greenhouse gases. As a part of this activity, the principal investigator is creating a thermoelectric lab module for an undergraduate course on internal combustion engines. This lab integrates thermoelectric devices into an engine's exhaust system, and thereby enables the study of waste heat conversion into electricity. The engine is also equipped with a dynamometer that characterizes its mechanical power. Hence students are able to measure the electric power produced by the thermoelectric devices as they relate to the primary engine variables: speed and torque. Technical AbstractThe goal of this project is to advance the thermoelectric materials field by combining three separate mechanisms to improve performance in nanocomposite materials. First, the microstructure of these composites consists of nanoparticles embedded in a matrix. This morphology promotes strong phonon scattering and favorable reductions in thermal conductivity. Second, quantum-confined nanocrystals are being used for the nanoparticle inclusions. This confinement causes sharp peaks in the electronic density of states, which leads to large thermoelectric power factors. Lastly, band convergence is being used to create a large effective band degeneracy, which further promotes large thermoelectric power factors. Colloidal nanocrystals and metal-chalcogenide cluster precursors are being combined as modular building blocks to create the nanocomposites. The local atomic and electronic structures of the nanocomposites are being characterized using an aberration-corrected scanning transmission electron microscope equipped with a high resolution electron energy loss spectrometer. A complete suite of thermoelectric property measurements (i.e. Seebeck coefficient, electrical conductivity, and thermal conductivity) is being performed on the nanocomposites over a broad range of temperatures. Collectively, this project's combination of novel nanocomposite formation, atomistic materials characterization, and thermoelectric measurement suite enables the targeted discovery of thermoelectric design rules for improved performance.