Optimization of high-energy ball milling process for uniform p-type Bi-Sb-Te thermoelectric material powder

Ball milling is widely used for producing powders of thermoelectric materials owing to its simplicity and scalability. In this research, we investigated the particle shape and size in p-type Bi-Sb-Te materials-the best-known and only commercially available thermoelectric materials at present-after high-energy ball milling. Although Bi-Sb-Te materials are known to be brittle, some ductile properties, such as particle agglomeration and welding, were observed. To avoid an increase in particle size via welding and to obtain particles with highly uniform sizes, two-step ball milling was performed and particle sizes were analyzed. The ball-milled powder was consolidated and sintered, and the resulting pellets showed no crystallographic orientation and consequently exhibited uniform thermal and electrical conductivities regardless of measurement direction.