Defect Engineering for More Reliable and Efficient p-type Thermoelectric Materials

The success of future manned NASA missions to the Moon depends critically on power generation capabilities. While planetary sunlight and temperature cycles complicate the use of solar panels and batteries, radioisotope thermoelectric generators (RTGs) are proven power sources with consistent, long-term power output largely independent of planetary conditions. RTGs produce power from a heat source surrounded by thermocouples made of n- and p-type thermoelectric materials. RTG performance is directly dependent on the heat-to-electricity conversion efficiency of the constituent thermoelectric materials. Currently PbTe-based materials have the highest reported efficiencies for typical planetary mission conditions. However, an unexplained onset of brittle behavior at high electronic doping levels occurs in p-type PbTe, but not in n-type PbTe. As a result, RTGs on recent NASA missions use alternative p-type materials with only half of PbTe’s efficiency, but better mechanical properties. A new class of high efficiency PbTe materials with improved mechanical properties will thus provide an immediate and massive increase in RTG power output.

This proposed research effort seeks to explain and overcome PbTe’s mechanical shortcomings by engineering 1D atomic vacancy point defects and 2D dislocation defects in PbTe. Newly proven experimental techniques to control vacancy concentrations will be applied to probe the influence of extrinsic dopants and defects on PbTe brittleness. A similar perspective will be applied in conjunction with advanced probe techniques to explain high p-type PbTe dislocation densities and their effects on mechanical and thermal properties. High temperature mechanical testing and long-term stability tests are proposed at each iteration of this careful defect engineering approach to ensure robust, reliable materials performance in typical RTG operating conditions.

This proposed research effort seeks to explain and overcome PbTe's mechanical shortcomings in radioisotope thermoelectric generators by engineering 1D atomic vacancy point defects and 2D dislocation defects in PbTe.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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