Microstructure composite-like Bi2S3 polycrystals with enhanced thermoelectric properties

Abstract

We have designed a composite-like microstructure to improve the thermoelectric (TE) properties of Bi₂S₃ polycrystals. The nanosized Bi₂S₃ powders derived from mechanical alloying (MA) were mixed with [001] oriented single crystalline Bi₂S₃ nanorods prepared by hydrothermal synthesis (HS), which were densified by spark plasma sintering (SPS) to form a composite-like microstructure bulk with road-like structures consisting of nanorods. Because the nanorods provide good electron transport paths, the carrier mobility of the composite-like Bi₂S₃ bulk materials was improved by more than two orders of magnitude by mixing 10 wt% nanorods into the MA-derived powders. The electrical resistivity was also reduced from 2.5 × 10⁻² to 8.5 × 10⁻⁴ Ωm at 323 K, but the thermal conductivity was just slightly increased, resulting in a significantly enhanced ZT value, which was almost two times higher than that of the nanorod-free sample. This study demonstrated the possibility to significantly enhance the ZT value of TE bulks by combining the advantages of single crystals and polycrystals via controlling the microstructure without any chemical doping.