Enhancement of Thermoelectric Properties by Magnetic Impurities in Lead-free Thermoelectric Materials

Thermoelectric technology has attracted a lot of attention because it enables eco-friendly power generation. The enhancement of thermoelectric performance is challenging due to its strong inverse interrelationship between electrical conductivity (σ) and Seebeck coefficient (S). In this study, we studied non-toxic IV-VI compound GeTe with magnetic impurities. Our experiments showed an improvement in thermoelectric performance by doping unfilled d-orbital elements. Some of unfilled d-orbital elements were added as magnetic impurities in the GeTe. Previously, we found that magnetic impurities generate exchange interaction and induce additional scattering, resolving their strong inverse correlation between electrical conductivity and Seebeck coefficient. The exchange interactions occur between the spin angular momentum of itinerant electrons and that of magnetic impurities. The exchange interaction between the spin angular momentum of magnetic impurities and itinerant electrons generates the superparamagnetic fluctuation inducing additional scattering reducing thermal conductivity. The magnetic impurities showed synergetic effects of the increasing powerfactor (S²σ) and decreasing thermal conductivity (κ) in zT = S²σT/κ resulting enhanced thermoelectric performance of GeTe.