Two-step strategy improves the wide-temperature-range thermoelectric performance of Mg3+xBi1.29Sb0.7Te0.01

Abstract

Mg3Bi2-based thermoelectric materials have attracted significant attention due to the absence of volatile and expensive chalcogen elements like Te, along with their potential for high thermoelectric performance near room temperature. However, stabilizing the Mg content and optimizing the preparation process remain key challenges in further improve their thermoelectric properties. In this study, we employ a two-step method to progressively enhance the near-room-temperature performance of Mg3Bi2-based thermoelectric materials. First, by fine-tuning the excess Mg, we achieve a p-to-n type transition, optimizing carrier concentration and mobility, which leads to a substantial improvement in the power factor. Next, by modifying the high-temperature sintering process to create a well-structured microstructure, we increase grain size without compromising system composition, further enhancing room-temperature electron mobility for faster electron transport. As a result, the room-temperature power factor of Mg3.4Bi1.29Sb0.7Te0.01 sintered at 1073 K significantly increases from 6.5 to 16 µW cm−1 K−2, while the figure of merit value at 300 K rises from 0.2 to nearly 0.5, with the peak figure of merit at 500 K approaching 0.9, ranking as one of the highest values reported for similar materials.