Recently, a team led by Jiaqing He (Chair Professor of Physics, SUSTech) successfully introduced the 2D Van der waals defects into the eco-friendly SnTe-based thermoelectric (TE) materials for the first time to enhance the average ZT value, which shed light for future studies on SnTe and other intermediate-temperature bulk TE materials. The results, entitled as “Constructing van der Waals gaps in cubic-structured SnTe-based thermoelectric materials,” have been published in one of the most famous international journals Energy & Environmental Science.

TE materials can convert heat into electricity directly. Owing to the advantages of appropriate size, high steady-state operation period, zero emission, and silence, the prospect of TE devices is promising for both military and commercial applications. At intermediate temperatures, tin telluride (SnTe), an analogue of the traditional PbTe TE system, is deemed to be the hotspot of TE field because of its earth-abundant, nontoxic and environment-friendly characteristics. However, it is noted that the TE conversion efficiency is not determined by the peak ZT but by the average ZT (ZTave) over the entire operating temperature range, which is still the bottleneck for SnTe-based materials.

Figure 1. The predicted structure diagrams of (a) Ge-Sb-Te, and (b) Sn-Sb-Te. (c) Comparison of ZT values of our work and reported data in SnTe system. (d) The average ZT values from 300 K to 800 K of this work and the reported work.

In this work, the team alloyed Sb2Te3 with SnTe, innovatively forming dense short-range gap-like structure in the matrix. Additionally, after doping with tiny content of Rhenium, a kind of larger and deeper gap-like defect could be observed, indicating that this introduced-like gap structure could migrate and reconstruct, contributing to stronger scattering of phonons. The experimental results, together with density functional theory (DFT) calculating results, revealed that fabricated Sb2Te3(SnTe)n samples resulted in optimized band structure and reduced lattice thermal conductivity. By optimizing the doping content, researchers can balance the influence of electrical and thermal transport parameters and achieve the purpose of enhancing thermoelectric performance.

Figure 2. (a) The false-color STEM HAADF images of Sb2Te3(SnTe)8 sample, (b) the selected area of a 1D Sn vacancy line, (c) the selected area of a 2D Sn vacancy gap. (d) and (e) are the simulated results of Sn vacancy line and gap in (c) and (d), respectively; (f) The false-color STEM HAADF images of Sb2Te3(Sn0.996Re0.004Te)8 sample, (g) the magnified area of the extended gap-like structure.