Enhancing Thermoelectric Properties of Polycrystalline Bi2S3 by Optimizing a Ball-Milling Process

Bismuth sulfide (Bi2S3) polycrystalline samples were fabricated by mechanical alloying (MA) combined with spark plasma sintering (SPS). The microstructure and electrical transport properties were investigated with special emphasis on the influence of the ball-milling process. Bi2S3 compound powders could be readily synthesized directly from elemental powders under all the investigated conditions, and highly dense n-type bulk Bi2S3 samples with high density (> 95%) were fabricated by the subsequent SPS process. Changing the MA conditions had no apparent influence on the microstructure or phase structure of the MA-derived Bi2S3 powders, but the electrical properties and thermopower of the SPS-sintered Bi2S3 bulk samples were greatly dependent on the MA speed and time. The power factor of Bi2S3 was increased to 233 mu W K-2 m(-1) at 573 K by optimizing the ball-milling process. This power factor is higher than values reported to date for Bi-S binary samples without texture.