Chinese scientists have realized important progress on the plasticization of inorganic thermoelectric semiconductors. This study, which was conducted by Prof. Xun Shi’s and Prof. Lidong Chen’s team from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, cooperating with the scientists from Hangzhou Institute for Advanced Study and Shanghai Jiao Tong University, was published online in Science on Dec. 06.（https://www.science.org/doi/10.1126/science.adr8450）

Inorganic semiconductors have abundant functionalities with high carrier mobility and good stability, which are the key components for modern electronics industry. However, theyare usually brittle, which greatly limits their application in flexible and deformable electronics. The recently discovered metal-like room-temperature plasticity/ductility in inorganic semiconductors reshapes the knowledge of material’s physical properties, but the types of plastic/ductile inorganic semiconductors are still very rare.

In this work, taking classic Bi₂Te₃-based thermoelectric semiconductors as examples, it is found that the defects, especially antisite defects, can lead to high-density, diverse microstructures to substantially influence mechanical properties and thus successfully transform these bulk semiconductors from brittle to plastic.

Bi₂Te₃-based semiconductors are the best TE materials near room temperature, which have been widely used for solid-state refrigeration, precise temperature control, and local thermal management. However, they are usually brittle and prone to break under mechanical loading.

Interestingly, the research team found that the Bi₂Te₃ bulk single crystals with the Bi:Te of 2.00:2.96 grown by using the temperature gradient method demonstrate extraordinary room-temperature plasticity. They can endure more than 20%, 8%, and 80% strains in the three-point bending, uniaxial tensile, and compression tests, respectively. These values are comparable with those of good plastic semiconductors and far larger than that in polycrystalline Bi₂Te₃-based materials.

The microstructure characterizations and molecular dynamic simulations indicate that the high-density, diverse microstructures (e.g. line defects: dislocation and ripplocation; planar defects: swapped-bilayer and hyperdislocation; and lattice distortions) induced bythe coexistence of antisite Bi_Te and Te_Bi defects are responsible for the extraordinary room-temperature plasticity. These high-density, diverse microstructures can facilitate the inter- and cross-layer slipping while maintaining structural integrity during deformation, to successfully transform the bulk semiconductors from brittle to plastic.

Likewise, the plastic defective Bi₂Te₃-based crystals also possess excellent thermoelectric performance, boosting the room-temperature zT of plastic thermoelectric semiconductors to 1.05, which is comparable with the best brittle thermoelectric semiconductors.

This groundbreaking work not only provides a novel high-performance plastic inorganic thermoelectric material but also proposes an effective strategy for transforming brittle materials into plastic ones, offering valuable insights for the plasticization of brittle inorganic non-metallic materials.

Fig. 1. Exceptional plasticity in defective Bi₂Te₃-based TE crystals.

Fig. 2. High-density, diverse microstructures in plastic Bi₂Te₃ crystal.

Fig. 3. Molecular dynamic simulations for defective Bi₂Te₃ crystal.