EAGER: CRYO: Development of Novel Ce1-xLaxB6 Thermoelectric Nanocomposites for Cryogenic Cooling

该项目由化学、生物工程、环境和运输系统部、土木、机械和制造创新部以及材料研究部共同支持。能够在超低温（1开尔文）下工作的冰箱，是运行量子设备所必需的。热电冰箱是固态热泵，使用电子作为热载体从冷却负荷中提取热量，它们通常比其他制冷技术具有实质性的优势。热电冰箱的一些更重要的特点包括没有活动部件，体积小，重量轻，精确的温度控制，电气“安静”操作，以及环保。然而，现有的热电材料在低温制冷方面效果不佳。普通金属的热电冷却在任何温度下都很弱。半导体在室温下是理想的热电材料，但在超低温下会变成电绝缘体。这个探索性研究早期概念基金（EAGER）项目的总体愿景是开发一种热电材料，可以在1开尔文的超低温下制冷。该项目的更广泛影响包括融入马里兰大学的教育活动，扩大代表性不足群体在研究中的参与，以促进多样性、公平和包容性，以及K-12的推广。该研究项目旨在开发新型Ce1-xLaxB6热电材料，以实现超低温制冷（1开尔文）。本文将探索在CeB6中掺杂非磁性镧（La），以降低电子输运中近田效应区向费米液体区转变的温度，从而使其峰值热电温度偏移1开尔文。此外，纳米复合技术将被用于提高单晶CeB6的品质系数，通过降低其声子热导率，同时保持其电子迁移率。马里兰大学最近开发的快速高温烧结方法将被用于制造各种掺杂的Ce1-xLaxB6热电纳米复合材料。为实现技术目标，制定了一系列相互关联的任务：1)Ce1-xLaxB6纳米复合材料的制备与优化；2) Ce1-xLaxB6纳米复合材料的微观结构及组成表征；Ce1-xLaxB6纳米复合材料的热电性能表征；4) Ce1-xLaxB6纳米复合材料的热电性能建模。热电材料的关键元素是铈和镧，它们在地球上的储量与许多常见的工业金属（如铜和铬）一样丰富。这项研究是整个雄心勃勃的高风险高回报议程中必要的第一个探索阶段。这种潜在的改变游戏规则的低温制冷技术的发展对量子器件的进步至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project is jointly supported by the Division of Chemical, Bioengineering, Environmental and Transport Systems, the Division of Civil, Mechanical and Manufacturing Innovation, and the Division of Materials Research.Refrigerators that can function at ultra-low temperatures, 1 Kelvin, are required to operate quantum-enabled devices. Thermoelectric refrigerators are solid-state heat pumps that use electrons as heat carriers to extract heat from the cooling load, and they often provide substantial advantages over alternative refrigeration technologies. Some of the more significant features of thermoelectric refrigerators include no moving parts, small size and weight, precise temperature control, electrically “quiet” operation, and environmentally friendly. However, the existing thermoelectric materials are not effective at cryogenic refrigeration. The thermoelectric cooling in normal metals is weak at any temperature. Semiconductors are ideal thermoelectric materials around room temperatures, but turn into electrical insulator at ultra-low temperatures. The overarching vision of this EArly-concept Grant for Exploratory Research (EAGER) project is to develop a thermoelectric material that can enable refrigeration at ultra-low temperatures, 1 Kelvin. The broader impacts of this project include its integration into educational activities at University of Maryland, broadening the participation of under-represented groups in research to foster diversity, equity, and inclusion, and K-12 outreach.This research program seeks to develop novel Ce1-xLaxB6 thermoelectric materials needed to enable ultra-low temperature refrigeration (1 Kelvin). In this effort, the doping of non-magnetic lanthanum (La) in CeB6 will be explored to lower the temperature of transition from the Kondo effect region to Fermi liquid region in electron transport, and therefore to shift its peak thermoelectric temperature 1 Kelvin. In addition, the nanocomposite technology will be employed to enhance the figure-of-merit of the single crystalline CeB6 by reducing its phonon thermal conductivity while preserving its electron mobility. The rapid, high temperature sintering method recently developed at the University of Maryland will be adopted to manufacture the Ce1-xLaxB6 thermoelectric nanocomposites with various doping. To achieve the technical objectives, a series of interrelated tasks is formulated: 1) Manufacturing and optimization of Ce1-xLaxB6 nanocomposites; 2) Microstructure and composition characterization of Ce1-xLaxB6 nanocomposites; 3) Thermoelectric property characterization of Ce1-xLaxB6 nanocomposites; and 4) Thermoelectric property modeling of Ce1-xLaxB6 nanocomposites. The key elements in the thermoelectric materials are Cerium and Lanthanum, which are as abundant on Earth as many familiar industrial metals, such as copper and chromium. The research is a necessary first exploratory stage in an overall ambitious high-risk-high-payoff agenda. The development of this potential game-changing refrigeration technology at cryogenic temperatures is critical for the advancement of quantum devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.