Predicting the Structure and Stability of Thermoelectric Composite Interfaces in Deep-Space using In Situ Microscopy

NASA KY GF application (due 5/18/20) DRAFT Title: Predicting the Structure and Stability of Thermoelectric Composite Interfaces in Deep-Space using In Situ Microscopy Project dates: August 1, 2020 to July 31, 2021 DRAFT Abstract Power sources for space missions must survive the harsh conditions of deep space for years or even decades before they may begin to be utilized for their mission, yet the successful utilization of power source material depends closely on tiny structural features on the nanometer or even atomic scale, whose degradation during years spent in high-vacuum and varying temperature gradients may be very difficult to predict. NASA deep space missions rely on radioisotope power systems, in particular the radioisotope thermoelectric generator (RTG), for which the natural radioactive decay of plutonium dioxide fuel provides heat which is converted to electricity by thermoelectric materials. Traditionally, thermoelectric materials must optimize their figure of merit, ZT, with a compromise in transport properties so as to maximize the Seebeck coefficient, S, and electrical conductivity, σ, while minimizing thermal conductivity, κ. However, recent efforts have examined novel approaches to decoupling these transport properties by combining a high Seebeck coefficient matrix, with nanoparticle inclusions to increase phonon scattering, to dope the material, or to provide low electrical resistance pathways. A state-of-the-art example of such a composite recently developed by the Bux Group (JPL) makes just such a synergistic combination of a lanthanum telluride (La3-xTe4) matrix with nickel nanoparticle inclusions for which the resulting La3-xTe4-Ni composite shows ZTs of up to 1.9 at the 1000 °C operating temperature. Here we propose to determine the structure of the interfaces embedded within La3- xTe-Ni composites, and in particular the dual roles of heat and oxygen on the mechanisms and kinetics of interface degradation.