Synergistic enhancement of thermoelectric and mechanical properties in Bi-Sb-Te alloys collaborated by Zn based metal organic framework (ZIF-8)

Abstract

Thermoelectric materials hold significant promise as they can directly convert thermal energy into electrical energy. Despite the discovery of numerous new thermoelectric materials in recent years, bismuth telluride(Bi2Te3)-based materials continue to be the most suitable for large-scale commercialization. Presently, there is scope for further improvement in the average ZT value and conversion efficiency of Bi2Te3-based materials. This study presents the successful synthesis of Bi0.42Sb1.58Te3(BST) alloys and ZIF-8 with high porosity and adjustable pore size using the solid-phase sintering method and spark plasma sintering(SPS). This method facilitates the doping of Bi sites and produces several atomic clusters in the BST matrix, significantly optimizing the electrical and thermal transport properties of BST thermoelectric materials. The Bi sites undergo low-valent cation doping, and additional hole carriers are introduced to optimize the electrical conductivity. Moreover, a large number of atomic clusters in the BST matrix act as effective phonon scattering centers, enhancing phonon scattering and reducing lattice thermal conductivity. Additionally, ZńBi,Sb defects are observed as defect clusters around the nanopores, which further reduce the lattice thermal conductivity. Notably, the ZT of Bi0.42Sb1.58Te3/0.3 wt% ZIF-8 sample reaches 1.42 at 348 K, and the average ZT is as high as 1.16 in the temperature range of 300–500 K due to the synergistic optimization of thermal and electrical transport properties. Furthermore, the thermoelectric conversion efficiency of the single-leg device reaches 5.03% at ΔT=250 K, and the mechanical properties of the sample are significantly improved. Due to the fine grain strengthening effect, the hardness of the 0.3 wt% doped sample is 1.2 GPa, and its Young's modulus is 43 GPa, exhibiting significant improvement compared to the pure sample. The findings of this study are expected to provide valuable insights for the optimization of other thermoelectric materials.