As existing energy sources have been depleting at a fast pace, thermoelectric (TE) materials have received much attention in recent years because of their role in clean energy generation and conversion. Thermoelectric materials hold promise in terrestrial applications such as waste heat recovery. Bismuth selenide (Bi2Se3), lead telluride (PbTe), skutterudites CoSb3, and Bi-Sb alloys are among the widely investigated thermoelectric materials.
Synthesis of above mentioned thermoelectric materials in nanostructured form and their characterization were investigated. Highly crystalline Bi2Se3, undoped and indium (In) doped PbTe, unfilled and ytterbium (Yb) filled CoSb3 nanomaterials were synthesized using hydrothermal/solvothermal technique and Ca-doped Bi-Sb alloy was synthesized using ball milling method. The mechanism of indium doping to the PbTe matrix was investigated using X-ray diffraction, laser-induced breakdown spectroscopy (LIBS) and a first principle calculation. It was found that indium doping, at a level below 2%, is substitution on Pb site. The effects of the amount of sodium borohydride (NaBH4) as the reducing agent and the annealing treatment on the phase transition of CoSb3 were investigated. It was found that a sufficient amount of NaBH4 along with the specific annealing condition was needed for the formation of pure phase CoSb3.
Thermoelectric properties of Bi2Se3 and Ca-doped Bi85Sb15 were also investigated. A lower thermal conductivity and a higher Seebeck coefficient were achieved for a Bi2Se3 sample prepared in dimethyl formamide (DMF) at 200ยบC for 24 h as compared to bulk Bi2Se3. The decrease in thermal conductivity can be attributed to the increased phonon scattering at the interfaces of the nanostructures and at the grain boundaries in the bulk nanocomposite. The increase in the Seebeck coefficient of Bi2Se3 nanostructures is likely the result of the quantum confinement of the carriers in nanostructures. The effect of calcium doping on Bi85Sb15 nanostructures were investigated. It was found that 2% calcium doped Bi-Sb alloy showed the best TE efficiency due to the enhanced power factor and reduced thermal conductivity.
