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

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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.