Achieved breakthrough progress in the research of bismuth telluride-based plastic thermoelectric materials

Bismuth telluride (Bi2Te3)-based thermoelectric materials, which include Bi2Te3 itself as well as its pseudobinary solid solutions formed with Bi2Se3 and Sb2Te3, have already achieved widespread commercial applications in solid-state refrigeration, precise temperature control, and localized thermal management. However, Bi2Te3-based materials are inherently brittle and prone to cleavage fracture under external mechanical stress, severely limiting their application in fields such as flexible and microelectronics. Previously, the Shanghai Institute of Ceramics, Chinese Academy of Sciences, introduced a high-density and diversified microstructure into single crystals by leveraging the interaction between two types of intrinsic antisite defects (BiTe and TeBi), thereby innovatively achieving a transformation of Bi2Te3 crystals from brittle to ductile (Science 2024). Nevertheless, the mechanical properties and deformation capabilities of Bi2Se3 and Sb2Te3 crystals, as well as their pseudobinary solid solutions with Bi2Te3, remain unreported. It is also unknown whether these materials possess similar ductile characteristics to those of Bi2Te3 single crystals.

Recently, Researcher Qiu Pengfei, Researcher Shi Xun, and Associate Researcher Ming Chen from the Shanghai Institute of Ceramics, in collaboration with the Hangzhou Institute for Advanced Study of University of Science and Technology of China, revealed the correlation among intrinsic defects, microstructure, and mechanical properties in Bi2Se3 and Sb2Te3. They identified the chemical composition ranges in which the pseudobinary solid solutions Bi2(Te,Se)3 and (Bi,Sb)2Te3 exhibit both excellent plasticity and outstanding thermoelectric performance. The related findings, titled “Plasticity of Bi2Te3-family thermoelectric crystals,” were published in Nature Communications (2025) 16:5190. Zhe Li, a master’s student at the Hangzhou Institute for Advanced Study of University of Science and Technology of China, and Associate Researcher Tingting Deng are co-first authors of the paper.

The research team synthesized Bi2Te3, Bi2Se3, and Sb2Te3 crystals using the temperature-gradient method. Unlike Bi2Te3 crystals, both Bi2Se3 and Sb2Te3 crystals exhibit brittleness, with their maximum strain under three-point bending in the in-plane direction being less than 3%, significantly lower than that of Bi2Te3 crystals (>20%). Transmission electron microscopy characterization revealed that Bi2Te3 crystals contain a high-density and diverse array of microstructures, including interleaved layers, ripples, and stacking faults, whereas the atomic arrangements in Bi2Se3 and Sb2Te3 crystals are remarkably regular. These differences in microstructure originate from the distinct intrinsic defect characteristics of Bi2Te3, Bi2Se3, and Sb2Te3. Theoretical calculations show that when the formation energies of the two antisite defects, BiTe and TeBi, in Bi2Te3 are equal—at only 0.6 eV—the crystal can simultaneously host high concentrations of both BiTe and TeBi antisite defects, thereby giving rise to a high-density and diverse microstructure. In contrast, the formation energies of the antisite defects BiSe and SeBi in Bi2Se3 are equal at a higher value (~1.3 eV), making it difficult for these defects to coexist in large quantities. Although the formation energies of the antisite defects SbTe and TeSb in Sb2Te3 are also relatively low (~0.6 eV), they occur exclusively in regions extremely rich in tellurium, which is experimentally challenging to achieve. Consequently, no high-density and diverse microstructures have been observed in Bi2Se3 and Sb2Te3 crystals, and the materials exhibit brittle behavior.

Doping Sb or Se into Bi2Te3 will alter its intrinsic defect characteristics, thereby influencing its microstructure, mechanical properties, and thermoelectric performance. The research team synthesized a series of solid-solution compounds: Bi2(Te,Se)3 and (Bi,Sb)2Te3. Mechanical property tests conducted at room temperature show that as the amount of Sb or Se dopant increases, the crystal's plasticity gradually diminishes. When the Sb doping level is below 70% or the Se doping level is below 20%, the crystals exhibit excellent plasticity similar to that of Bi2Te3, with maximum bending strains along the in-plane direction reaching ≥10%. Transmission electron microscopy characterization reveals that the plastic Bi2(Te,Se)3 and (Bi,Sb)2Te3 crystals also feature high-density and diversified microstructures, further confirming their close correlation with plasticity. Thermoelectric property tests indicate that Sb doping significantly increases the hole concentration in Bi2Te3 crystals, while Se doping shifts the dominant charge carriers from holes to electrons. Meanwhile, both Sb and Se doping effectively reduce the lattice thermal conductivity. Based on the comprehensive results from mechanical and thermoelectric property tests, we have constructed a phase diagram illustrating the relationship among composition, plasticity, type of electrical conductivity, and thermoelectric performance for Bi2(Te,Se)3 and (Bi,Sb)2Te3 crystals. When the Sb doping level ranges from 0 to y < 0.7, the crystals simultaneously exhibit p-type electrical conductivity, excellent plasticity, and high thermoelectric performance, with maximum bending strains along the in-plane direction reaching ≥10%, power factors PF ≥ 20 μW cm−1K−2, and thermoelectric figure of merit zT ≥ 0.6.

This study has broadened the research scope of Bi2Te3-based ductile inorganic thermoelectric materials and deepened the understanding of the correlation among defects, microstructure, and mechanical properties in thermoelectric materials. It holds significant value in guiding the research on new high-performance ductile inorganic thermoelectric materials.

This research was supported by the National Key R&D Program, the National Natural Science Foundation of China, and the Chinese Academy of Sciences' Young Team Program for Stable Support in Basic Research.

Paper link: https://doi.org/10.1038/s41467-025-60465-2

Figure 1: Relationship among compositional, plasticity, conductivity type, and thermoelectric properties of Bi2(Te1-xSex)3 and (Bi1-ySby)2Te3 crystals at room temperature

Figure 2: Defect formation energies of Bi2Te3, Bi2Se3, and Sb2Te3, as well as the formation energies of microstructures at different scales induced by two types of antisite defects in Bi2Te3.