Bi₂Te₃-family thermoelectric (TE) materials, including Bi₂Te₃, Bi₂Se₃, Sb₂Te₃, and their pseudo-binary solid solutions semiconductors, are widely used for solid-state refrigeration, precise temperature control, and local thermal management. However, it is widely recognized that the Bi₂Te₃-family TE materials are brittle and prone to break under mechanical loading,which greatly limits their application in flexible and micro-electronics. In prior work, researchers from Shanghai Institute of Ceramics show that the antisite defects can lead to high-density, diverse microstructures in classic bulk semiconductor Bi₂Te₃, which can substantially affect mechanical properties and thus successfully transform itfrom brittle to plastic (Science 2024). Nevertheless, Bi₂Se₃, Sb₂Te₃, and their pseudo-binary solid solutions with Bi₂Te₃ might possess distinct plasticity with that of Bi₂Te₃ at room temperature, but the related investigation has not been reported yet.

(https://doi.org/10.1038/s41467-025-60465-2)

Recently, the researchers from Shanghai Institute of Ceramics, in collaboration with the Hangzhou Institute for Advanced Study, further clarified the relationship among the native defects, microstructures, mechanical properties of Bi₂Se₃, Sb₂Te₃, and their solid solutions with Bi₂Te₃. Firstly, the Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ bulk crystals were grown by the temperature gradient method. The Bi₂Se₃ and Sb₂Te₃ crystals have an engineering strain less than 5% along the in-plane direction in the three-point bending test. This value ismuch lower than those of the Bi₂Te₃ crystals (> 20%), indicating their poor plasticity. Scanning transmission electron microscopy characterizations reveal that the Bi₂Se₃ and Sb₂Te₃ bulk crystals have highly regular atomic arrangements, which are different with the existence of high-density, diverse microstructures in bulk Bi₂Te₃ crystals. Such difference is found to be originated from the different dominant native defects in these three compounds. In Bi₂Te₃, when the defect formation energies of Bi_Te and Te_Bi antisite defects are the same, the corresponding value is about 0.63 eV. In Bi₂Se₃, when the defect formation energies of Bi_Se and Se_Bi antisite defects are the same, the corresponding value is about 1.32 eV. In Sb₂Te₃, only when the anion chemical potential is tuned to the vicinity of the extreme Te-rich point, Sb_Te and Te_Sb can own the same formation energy. However, in experiment, this point is difficult to be achieved. Thus, in either Bi₂Se₃ or Sb₂Te₃, the antisite defects are difficult to coexist, leading to the highly regular atomic arrangements as well as poor plasticity.

Then, a series of Bi₂(Te_1-xSe_x)₃ and (Bi_1-ySb_y)₂Te₃ bulk crystals are grown by the temperature gradient method. Room-temperature mechanical property measurements indicate that the plasticity is significantly decreased with increasing the Se/Sb content in Bi₂Te₃. When y < 0.7 or x < 0.2, the maximum bending strain is over 10% along the in-plane direction andthe crystals exhibit excellent plasticity comparable to that of Bi₂Te₃. Microstructure characterizations show that there are still high-density, diverse microstructures in plastic Bi₂(Te,Se)₃ and (Bi,Sb)₂Te₃. In addition, with increasing the Sb-alloying content, the hole concentration in Bi₂Te₃ crystals is gradually increased, while Se alloying converts the majority carrier type from holes to electrons. Furthermore, with increasing the Sb/Se alloying content in Bi₂Te₃, the lattice thermal conductivity is greatly reduced. Combining the measured maximum strains in the three-point bending test and the measuredroom-temperature power factor (PF) and TE figure-of-merit (zT), the composition range for the Bi₂(Te_1-xSe_x)₃ and (Bi_1-ySb_y)₂Te₃ bulk crystals that simultaneously possess exceptional plasticity with  the maximum bending strain > 10%, high PF > 20 μW cm⁻¹K⁻², and high zT > 0.6 is determined as 0 ≤ y  <  0.7.

This work not only expands the research scope of plastic inorganic thermoelectric materials based on Bi₂Te₃, but also provides a deep understanding on the relationship among native defects, microstructures, and mechanical properties in thermoelectric materials. The related findings were published in Nature Communications (2025).

This work was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, and the Chinese Academy of Sciences Project for Young Scientists in Basic Research.

Fig. 1 Room-temperature plasticity, conduction behavior, power factor (PF), and figure-of-merit (zT) for Bi₂(Te_1-xSe_x)₃ and (Bi_1-ySb_y)₂Te₃ bulk crystals.

Fig. 2 Formation energy of native defects in Bi₂Te₃, Bi₂Se₃, Sb₂Te₃ and the formation energy of different defective structures in Bi₂Te₃ relative to that containing isolated antisite defects.

Contact: Pengfei Qiu

Shanghai Institute of Ceramics Chinese Academy of Sciences

E-mail: qiupf@mail.sic.ac.cn