A two-step strategy improves the wide-temperature-range thermoelectric performance of Mg_3+xBi_1.29Sb_0.7Te_0.01

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 improving 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 the system composition, further enhancing room-temperature electron mobility for faster electron transport. As a result, the room-temperature power factor of Mg_3.4Bi_1.29Sb_0.7Te_0.01 sintered at 1073 K significantly increases from 6.5 to 16 μW cm⁻¹ K⁻², while the figure of merit value at 323 K increases from 0.2 to nearly 0.5, with the peak figure of merit at 500 K approaching 0.9, reaching one of the highest values reported for similar materials.