KY EPSCoR: Determining the Structure of Thermoelectric Materials in Real-time Using Single-atom Resolution and in Situ Imaging

Radioisotope thermoelectric (TE) generator technology plays a critical role for power generation in space, and the development of high efficiency TE materials which can operate at very high temperatures is therefore critical to the space exploration needs of NASA. TE materials are designed, and their efficiencies controlled, by harnessing simple structure-property relationships, for example to maximize electronic conductivity while simultaneously reducing thermal conductivity. Designing materials to take advantage of these structure-property relationships requires detailed knowledge of each structure, not only for many potential synthetic parameters, but also as these structures change over time, for example during their initial growth, or during their use in devices. Thus, there is a critical need for the development of local probe techniques which cannot only characterize these materials at ultra-high resolution, but additionally perform such characterization under conditions of temperature and pressure which mimic the synthesis and operating environments. In the absence of such methods, the development of novel TE materials to meet the high efficiencies required for power generation during the exploration of space will likely remain challenging. We propose to develop in situ high-resolution transmission electron microscopy (TEM) techniques for the investigation of two prototypical TE material systems. The first is a series of oxides with the Zintl structure, and are already known to be promising from an ongoing collaboration with NASA Glenn Research Center. These materials depend critically, however, on features such as secondary-phases and voids, which develop during synthesis and operation at high temperature, yet the mechanisms and driving forces for the formation of such features are not well-understood. The second set of materials under investigation are a series of alloys whose properties are still in the exploration phase, but whose structure suggests will make excellent TEs. These materials are the focus of a new collaboration between our group at UK, Dr. Julia Chan’s group at UT Dallas, and our collaborators at NASA Glenn, the group of Dr. Fred Dynys. The experiments proposed herein will build on our existing UK-NASA Glenn collaboration, to position our work for successful submission to the NASA RA program and other multi-year awards.