In the realm of thermoelectric materials, a persistent puzzle has been the donor-like effect, a phenomenon that causes an uncontrollable increase in electron density, significantly impacting the performance of both p-type and n-type polycrystalline bismuth-telluride-based materials. This effect has long baffled researchers, but a groundbreaking study led by Feng Liu at Zhejiang University’s State Key Laboratory of Silicon and Advanced Semiconductor Materials has finally shed light on its origins.
The study, published in Small Science, reveals that the donor-like effect in bismuth-telluride-based polycrystals is not due to the commonly assumed factors but rather a result of oxygen adsorption-induced evolution of point defects. “The dominant point defect in stoichiometric zone-melted Bi2Te3 ingot is the acceptor-like Bi′Te,” Liu explains. “However, during the fabrication of high-strength polycrystals, exposure to air leads to oxygen absorption and the formation of a secondary phase, Bi2TeO5, during sintering. This alters the local chemical equilibrium, promoting the evolution of intrinsic point defects from acceptor-like Bi′Te to donor-like TeBi•.”
This discovery is a game-changer for the thermoelectric industry. By understanding and controlling the evolution of these point defects, researchers can now minimize the donor-like effect, leading to more stable and efficient thermoelectric materials. Liu’s team demonstrated this by achieving a reproducible high zT value of 1.0 at 325 K in Bi2Te2.7Se0.3-based polycrystals, a significant milestone in the field.
The implications of this research are vast, particularly for the energy sector. Thermoelectric materials convert heat into electricity, making them crucial for waste heat recovery in industrial processes and automotive applications. By improving the performance and stability of these materials, the study paves the way for more efficient energy conversion systems, reducing reliance on fossil fuels and lowering greenhouse gas emissions.
The findings also underscore the importance of precise fabrication processes. “If the fabrication process is strictly controlled to minimize oxygen adsorption, the evolution of the point defects will be avoided, and the donor-like effect disappears,” Liu notes. This insight could revolutionize the way thermoelectric materials are produced, ensuring higher quality and performance.
As the world continues to seek sustainable energy solutions, this research offers a beacon of hope. By unraveling the mystery of the donor-like effect, Liu and his team have opened new avenues for developing high-performance thermoelectric materials, potentially transforming the energy landscape. The study, published in Small Science, marks a significant step forward in the quest for efficient and reliable thermoelectric technologies.