Disproportionation of thermoelectric bismuth telluridenanowires as a result of the annealing process

Abstract

P-type thermoelectric bismuth telluride nanowires were fabricated by pulsed electrodeposition in anodic aluminium oxide (AAO) membranes. Subsequently, the nanowires were annealed at 423, 523 and 673 K in an inert atmosphere for 4 h. With increasing temperature, it was observed that the Te compound incongruently sublimates due to its high vapor pressure, leading to disproportionation (from Bi₂Te₃ to Bi₄Te₃via Bi₄Te₅). The crystalline structure of the nanowires was then investigated using XRD and SAED, with nanowire compositions investigated using an EDX attached to a TEM. The crystallinity of the nanowires was found to be enhanced with increased annealing temperature, and nanowires annealed at 673 K were stably maintained in the Bi₄Te₃ phase. Additionally, the Seebeck coefficient was determined and the thermopower of nanowires annealed at a temperature of 423 K was shown to be slightly enhanced. Significantly suppressed Seebeck values for annealing temperatures of 523 K and 673 K were also observed.