Effects of mechanical alloying process on thermoelectric properties of Bi2S3 Bulk

Abstract

Bismuth sulfide (Bi2S3) polycrystalline bulks are fabricated by spark plasma sintering (SPS) combined with a mechanical alloying (MA) process. The electrical transport properties are investigated with a special emphasis on dry-milling speed, wet-milling time and mediums in MA process. The phase structure, the microstructure, and the electrical/thermal transport properties for the bulk samples are measured. The results suggest that the second Bi2O3 phase is formed because of the micro-oxidation when the wet medium is fixed to absolute ethyl alcohol, which refines the grain sizes and affects electrical transport properties of the bulk samples. Prolonging the wet-milling time in absolute ethyl alcohol causes the increase of resistivity and the decrease of the power factor. The electrical transport properties degrade due to the porous microstructure in bulk samples even without oxidization as the acetone is used as a milling medium. The largest ZT value 0.25 is obtained at 573 K for the samples dry-milled under 425 r/min for 15 h without wet-milling, which is the highest value in the reported values so far.