Unlocking High-Performance Thermoelectrics: From Phase Engineering to Entropy-Enhanced Materials

In the rapidly evolving field of thermoelectric materials, significant strides have been made to improve material properties and energy conversion efficiency. This talk will traverse multiple avenues of cutting-edge research to showcase advancements in our group in thermoelectric materials and applications. We will present our efforts on Ga-doped n-type PbTe thermoelectric materials that undergo dynamic phase conversion through Cu2Se alloying. The addition of Cu2Se enhances electrical transport properties while reducing lattice thermal conductivity. At elevated temperatures, the material undergoes dynamic changes in its phase compositions, achieving a promising ZT for n-type systems of ~1.63 at 823 K for intermediate-temperature applications. Transitioning to p-type lead chalcogenides, these materials exhibit superior thermoelectric performance due to valence band convergence. Improvements on n-type materials are more difficult because of the absence of easy electronic band convergence. However, introducing GaSb doping into their n-type counterparts has led to significant improvements as well. This intervention causes conduction band convergence and increases the average power factor, culminating in a high ZT of across a wide temperature range. Building on our previous results, we have also explored the fascinating realm of entropy-engineered materials, using the PbGeSnCdxTe3+x family as a case study. The high-entropy effect from alloying not only stabilizes the material's cubic phase but also significantly improves thermoelectric properties to a maximum ZT of 1.63 at 875 K. PbS-based compounds are less well-developed by can become key players in this arena. By alloying PbS with GeS, we achieved a multi-tiered optimization of its electrical and thermal transport properties, involving Ge2+ substitution, the formation of a secondary phase of Pb5Ge5S12, and enhanced electron mobility. The resultant 14% GeS-alloyed samples yield a ZT of 1.32 at 923 K, outperforming standard Sb-doped PbS by approximately 55% and setting a new benchmark for n-type PbS-based thermoelectric systems. This presentation aims to provide new insights and spark interdisciplinary discussions on optimizing thermoelectric materials for a sustainable energy future.