Spark Plasma Sintering Effect on Thermoelectric Properties of Nanostructured Bismuth Telluride Synthesized by High Energy Ball Milling.

Thermoelectric properties of high energy ball milled nano structured bismuth telluride (Bi₂Te₃) have been reported. By high energy ball milling, alloyed bulk crystalline ingots crush into nanopowder and followed by spark plasma sintering (SPS), we have demonstrate high figure of merit (ZT) in bismuth telluride pellet samples. In this work systematic study carried out on three pellet samples of Bi₂Te₃, synthesized by high ball milling for the time period of 4 hours, 8 hours and 12 hours and followed by SPS at the same processing parameters. A peak value of dimensionless figure of merit of about 1.22 at the temperature of 473 K has been achieved for 8 hours ball milled pellet sample. This enhancement in ZT value is mostly due to decrease in thermal conductivity. Results of this study demonstrate that ball milling and SPS has a major effect in controlling the density of grain boundaries of Bi₂Te₃ nano particles, while the pressure exerted on the powder samples during SPS introduce stress at the boundaries of the crystallites. These disordered crystallite boundary regions exert scattering of thermal energy carriers which reduced the thermal conductivity of the materials.