Thermoelectric materials can directly convert thermal energy available in waste heat into electrical energy. This EArly Concept Grant for Exploratory Research (EAGER) provides funding for the development of bulk shapes of high performance nanostructured thermoelectric materials. A novel spark plasma sintering (SPS) process will be used to sinter mechanically alloyed nanostructured powder of thermoelectric compositions into bulk shapes. The SPS process will involve simultaneous application of uniaxial pressure and pulsed direct current to nanostructured powder placed in the graphite dies. The investigations of this proposal will be focused on bulk nanostructuring of bismuth telluride- and lead telluride-based compositions of thermoelectric materials. Major emphasis of the research plan will be on investigating the fundamental densification mechanisms of nanostructured thermoelectric powder during SPS and the dependence of thermoelectric performance on grain/feature size in nano-scale range (< 50 nm).
Successful completion of this project will significantly advance the state-of-the-art in nanostructuring of bulk thermoelectric materials for improving the performance of these materials. The proposed investigations will provide valuable information about the influence of grain size on the thermoelectric performance which is important for optimizing the performance these materials. Since large amounts of materials are needed for energy conversion, the possibilities of fabricating bulk shapes of the nanostructured thermoelectric materials using SPS is expected to accelerate utilization of these materials in real-world thermoelectric devices. The proposed EAGER plan will provide research experiences and training to graduate and undergraduate students, and prepare them for future career in this important field of energy materials. The results of the proposed research will also be incorporated in the graduate course on Modern Materials to achieve the broader impact.
can directly convert thermal energy into electrical energy and, reversibly, electrical energy into thermal energy. Nanostructured materials are attractive for many applications in solid-state cooling and power generation. However, bulk processing of these nanostructured materials is challenging. This project developed a processing approach based on mechanical alloying and spark plasma sintering for the fabrication of nanostructured Ag-Pb-Sb-Te based nanostructured thermoelectric materials. The mechanical alloying enabled the processing of starting elemental powder into homogeneous alloy powder with uniform elemental distribution. The subsequent spark plasma sintering allowed the sintering of monolithic discs without significant grain growth and re-distribution of major elements. The monolithic discs of diameter 10 mm and thickness 5 mm were successfully sintered at 400 C using the proposed approach. The microstructural analysis indicated compositional uniformity and the fine grained structure for the sintered discs. The processing parameters, mainly ball milling parameters have significant effect on the cracking tendency of the sintered discs. To accomplish broader impact of these nanostructured alloys, further scalability of the approach needs to be demonstrated. The project provided hands-on processing (mechanical alloying and spark plasma sintering) and characterization (x-ray diffraction, scanning electron microscopy, and elemental analysis) opportunities to graduate students. The results of the project were also discussed in the graduate courses for broader dissemination.
