Crystal Chemistry and Properties of Zintl Phases: Towards Efficient New Thermoelectrics

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PART 1:   NON-TECHNICAL SUMMARYThe synthesis of new compounds and crystal structures remains an extremely important fundamental research endeavor in the pursuit of new technologically relevant materials. This research, funded by the Solid State and Materials Chemistry Program targets the synthesis of new compounds with technological applications, specifically thermoelectric applications. Thermoelectric materials can convert a heat gradient into electricity. The design of efficient thermoelectric devices is a major goal for energy conversion technologies. Zintl phases, which are a subset of intermetallics are ideal candidates for thermoelectric applications as they are semiconductors with complex structures which provide low thermal conductivity, which allows for precise tuning of carrier concentration. In this structure-property relationship study specific Zintl structures will be targeted to test ideas for property outcomes based on atomic-level modifications. The long-term goal is to discover new highly efficient thermoelectric materials. Short term goals include building an understanding of best Zintl structures for efficient thermoelectric energy conversion and discovery of new magnetic and electronic properties for other technological applications. With this NSF grant the principal investigator helps educate the next generation of the STEM workforce. Students from high school through graduate school are provided hands-on training and their scientific and social skills are developed through workshops and individual mentorship. The next generation of scientists is trained to consider novel materials and their impact on technology for our future energy needs and specifically thermoelectrics.PART 2:   TECHNICAL SUMMARYThis grant supports fundamental research efforts to prepare new Zintl phase compounds and measure their properties with a goal of discovering new thermoelectric materials and enhancing their thermoelectric properties. The research focuses on studying a) new variants of 14-1-11 Zintl phases for which high zT is expected at high temperatures, and b) novel Europium-based materials exhibiting low thermal conductivity. New compounds are synthesized as single crystals, high purity powders and pellets via flux, metallurgical routes, and spark plasma sintering. A suite of physical characterization techniques is utilized, including single crystal and powder X-ray diffraction, electron microprobe, electrical and magnetic measurements. Structure and phase composition is subsequently correlated with electronic and thermal transport properties. With this NSF grant the principal investigator mentors science students starting their science careers in high school to undergraduates in partnerships with graduate students, ultimately providing professional training for scientific careers. Students are provided hands-on training and their scientific and social skills are developed through workshops and individual mentorship. The research is presented at national and international meetings and the findings published in peer-review journals.