Grain boundary engineering simultaneously optimized thermoelectric and mechanical properties of BiSbTe alloys

The Bi2Te3-based alloys with atomically layered structure are the best thermoelectric performance at the vicinity of room temperature. However, the inferior mechanical properties due to weak van der Waals interactions between layers are the obstacle to further promote the widespread commercialized application. Here, the grain refinement BiSbTe alloys prepared by ball milling and spark plasma sintering (grain boundary engineering) is reported. The microstructure characterization results indicate that ball milling can significantly reduce the grain size. The grain boundary engineering can significantly improve Seebeck coefficient about 23 %, maintain large hall mobility and reduce the carrier thermal conductivity about 48 %, and the lattice thermal conductivity is slightly decreased about 15 % by enhanced grain boundary phonon scattering. The highest average ZT reaches 1.2 in the range of 300–400 K for grain refinement sample, which is beneficial to improve the conversion efficiency of thermoelectric devices, and the Vickers hardness of the corresponding sample is increased by 58 %. The easy-to-operate strategy of grain refinement caused by ball milling provides a way to mass produce high performance and robust mechanical properties Bi2Te3-based thermoelectric devices. •The grain boundary engineering can significantly reduce thermal conductivity.•The coordinated regulation of electro-thermal-mechanical properties was achieved.•Our work provides a method to the large-scale production of Bi2Te3 alloys.•The high Vickers hardness can promote the development of thermoelectric devices.