Effects of Synthesis Parameters and Thickness on Thermoelectric Properties of Bi2Te3 Fabricated Using Mechanical Alloying and Spark Plasma Sintering

Bi2Te3 compound has been shown to exhibit the highest thermoelectric figure of merit at 573 K to 673 K. Bi2Te3 samples were synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS) in this work. The effects of the milling and SPS parameters as well as the specimen thickness were evaluated to obtain the best microstructural and thermoelectric properties. To synthesize Bi2Te3, Bi and Te powders were mechanically alloyed under argon atmosphere in a stainless-steel vial with a ball-to-powder weight ratio of 15:1 for different durations. The synthesized powders were then sintered using SPS at different temperatures. To characterize the Bi2Te3 powders and bulk samples, x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analysis were applied. Furthermore, the bandgap energy was measured by ultraviolet–visible (UV–Vis) spectroscopy. Moreover, the Seebeck voltage and electrical conductivity were determined at different temperatures. The experimental results illustrate that, by enhancing the sintering temperature from 623 K to 673 K, the maximum Seebeck coefficient was increased from 136 μV/K to 156 μV/K. To investigate the effect of thickness, specimens were sintered at the optimum temperature of 673 K with thicknesses of 1 mm, 1.5 mm, 2 mm, 3 mm, and 4 mm. The results showed that, by decreasing the thickness, the maximum Seebeck coefficient was increased from 144 μV/K to 166 μV/K while the electrical conductivity was increased from 0.35 × 105 S/m to 1.42 × 105 S/m, resulting in an increase in the power factor from 0.76 mW/m-K2 to 3.94 mW/m-K2.