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

Abstract

Bi 2 Te 3 compound has been shown to exhibit the highest thermoelectric figure of merit at 573 K to 673 K. Bi 2 Te 3 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 Bi 2 Te 3 , 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 Bi 2 Te 3 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 lV/K to 156 lV/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 lV/K to 166 lV/K while the electrical conductivity was increased from 0.35 9 10 5 S/m to 1.42 9 10 5 S/ m, resulting in an increase in the power factor from 0.76 mW/m-K 2 to 3.94 mW/m-K 2 .

Thermoelectric Ag2Se: Imperfection, Homogeneity, and Reproducibility

“…Besides, the Ag + migration and the fast fusing of nanosized MA powder during the SPS process can also play a role. Large porosity by mechanical alloying has also been found in other materials such as Bi 2 Te 3 , and PbSe …”

“…Besides, the Ag + migration 45 and the fast fusing of nanosized MA powder 33 during the SPS process can also play a role. Large porosity by mechanical alloying has also been found in other materials such as Bi 2 Te 3 46,47 and PbSe. 48 Three-dimensional atom probe tomography (3D APT) mapping elaborately demonstrates the abundant nonuniformity of these samples on the nanometer scale.…”

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“…Nonetheless, it shows a Seebeck coefficient of ≈1.38 mV K −1 , which exceeds the majority of previously reported works. [ 68,69 ] If Tg is performed by maintaining a higher relative humidity, both ion and electron charges travel concurrently and synergistically within the conductive layer to generate HTE. Additional experiments were conducted to determine their synergistic working mechanisms utilizing 10–95% relative humidity, and temperatures range from 10 to 50 °C (Figure 5a).…”