Structural and thermoelectric studies of Sb2te3 and Bi2te3 - based chalcogenide alloys and nanocomposites

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PhD; 2023; Physics

Thermoelectricity is one of the potential solutions for the rapidly increasing energy demand. Thermoelectric generators can turn waste heat into usable energy. Due to their effectiveness in the 300 K to 500 K temperature range, Sb2Te3 and Bi2Te3 are two of the most researched thermoelectric materials. These thermoelectric materials that operate at room temperature can have their thermoelectric performance improved through doping, nanostructuring, orientation engineering, and nanocomposites, among other techniques. Due to their capacity to lower thermal conductivity (κ) while maintaining a high-power factor (PF=S2σ), nanocomposites and doping techniques have garnered the most attention among them. The rate of melt solidification has recently been demonstrated to have the ability to dramatically adjust the thermoelectric characteristics to a greater extent. The thermoelectric characteristics of Sb2Te3/Te nanocomposites and Bi2Te3 alloy were examined in the first section of this thesis. This work has shown that the rate of melt solidification has a substantial impact on the structural and thermoelectric properties. It has been demonstrated that the optimum way to get better thermoelectric performances is with moderate melt quenching rates (normal water and ice water quenching). The thermoelectric properties of nanocomposites made by combining Sb2Te3 and poly methyl methacrylate (PMMA) have been studied in the second section of the thesis. For polymer nanocomposites, thermal conductivity was found to be significantly reduced. A 30% reduction in thermal conductivity has been seen with 5% polymer composites. In the last part of the thesis, the effect of Zn doping on Sb2Te3 has been studied. The prepared powder samples were sintered by spark plasma sintering (SPS). An increase in Zn doping increased the power factor considerably because Zn+2 doping in place of Sb+3 in Sb2Te3 acts as an acceptor. It increases p-type carrier concentration and thereby enhances the electrical conductivity. The thermoelectric figure of merit was found to increase by 12 % for the Zn-doped Sb2Te3. The zT of the SPS sintered Zn-doped Sb2Te3 is increased by 80% compared to the as-prepared Sb2Te3 ingot. The results presented in this thesis demonstrate that the zT of thermoelectric materials can be modulated by using different melt solidification rates, doping, and by forming nanocomposites.