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Methods of making half-Heuslers based thermoelectric material with enhanced figure of merit.
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Summary Our inventors have developed methods to improve the peak ZT of half-Heuslers based thermoelectric material at 700 degree Celsius to be 0.8. Background Thermoelectric (TE) generator, converting waste heat to electricity, has received increasing attention due to their role in reducing CO2 and greenhouse emission. The efficiency of TE generator relies on TE materials with both high electrical conductivity and low thermal conductivity, so the material can generate a large voltage but remain hot at one side and cold at the other side. The efficiency of the TE material can be determined by the dimensionless thermoelectric figure-of-merit (ZT), where a ZT value of about 1 has been a benchmark for many thermoelectric materials. The higher the ZT the more efficient the material is. Current common TE materials, including bismuth telluride (Bi2Te3), lead telluride (PbTe), and silicon germanium (SiGe), are all very expensive compounds due to the rare elements inside. Therefore, high efficiency and cost-effective TE material is desired to fill the need. Invention Our inventors at Boston College have developed several novel TE materials through nanocomposite approach using ball milling and hot pressing. They have improved the peak ZT of Half-Heuslers to be 0.8 at 700 °C. They also developed another p-type TE material, Tl0.02Pb0.98Te1-xSexSi0.02Naz (x has a value from 0 to 1, z has a value of 0.015, 0.020, or 0.025), with strong mechanical strength and yield higher ZT values of ~1.7 at 770 K, which enables the application of such materials in waste heat recovery at temperature close to 500 o C. In addition, our inventors have developed methods to improve thermal conductivity with nanotechnologies and to synthesize TE material from chalcogens and transition metals.