Researchers Qiu Pengfei, Shi Xun, and Chen Lidong from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, along with their collaborators, have achieved a transformation of brittle bismuth telluride (Bi2Te3)-based materials from brittle to ductile by modulating anti-site defects to induce the formation of high-density and diversified microstructures. This breakthrough has boosted the room-temperature thermoelectric figure of merit of ductile thermoelectric materials to approximately 1.0. The relevant findings were recently published in "Science."
▲ (A) Three-point bending stress-strain curves and (B) thermoelectric properties of plastic Bi2Te3 crystals with high-density/diverse microstructures
At room temperature, inorganic nonmetallic materials typically exhibit brittleness, making them difficult to machine precisely like metals and prone to sudden fracture and failure. Currently, bulk inorganic nonmetallic materials with intrinsic plasticity are relatively rare, and their thermoelectric performance is significantly lower than that of conventional brittle materials.
Bi2Te3-based materials are the best thermoelectric materials in the room-temperature range, but they are typically brittle. Due to the similar atomic radii and electronegativities of Bi and Te, Bi2Te3-based materials tend to form high-concentration intrinsic defects, which in turn induce the formation of high-density and diversified microstructures, thereby affecting the material's mechanical properties.
The research team prepared bulk single crystals of Bi2Te3 with precisely controlled stoichiometry using the temperature-gradient method, demonstrating excellent plastic deformation capability. Transmission electron microscopy characterization revealed a high-density and diversified microstructure in the Bi2Te3 single crystals, which originates from the transformation of BiTe and TeBi anti-site defects. By employing molecular dynamics simulations, the research team elucidated the impact of this microstructure on mechanical properties, proving that this microstructure is a key factor underlying the plasticization of Bi2Te3 single crystals.
The research team found that plastic Bi2Te3 single crystals exhibit excellent thermoelectric performance, with room-temperature power factors and thermoelectric figures of merit significantly higher than those reported for other plastic thermoelectric materials. By using solid-solution Sb doping to regulate carrier concentration, they not only maintained excellent plasticity but also further enhanced the room-temperature power factor and thermoelectric figure of merit.
Finally, the research team selected plastic Bi0.8Sb1.2Te3 single crystals and Ag2Se0.67S0.33 as p-type and n-type thermoelectric legs, respectively, and fabricated 8 pairs of flexible thermoelectric devices with a Y-shaped structure. When worn on the human body at an ambient temperature of 19℃, the device achieved a maximum normalized power density of 2.0 μW/cm², significantly higher than that of devices based on other plastic thermoelectric materials.
This study not only develops a new type of high-performance, plastic inorganic thermoelectric material but also provides an effective strategy for transforming brittle materials into plastic ones, offering important insights for the plasticization research of brittle inorganic nonmetallic materials.
Relevant paper information:
https://doi.org/10.1126/science.adr8450
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