Synthesis and Characterization of Thermoelectric Nanomaterials

Authors

Kamal KadelFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Physics

First Advisor's Name

Wenzhi Li

First Advisor's Committee Title

Major Professor

Second Advisor's Name

Yesim Darici

Third Advisor's Name

Chunlei Wang

Fourth Advisor's Name

Xuewen Wang

Keywords

Nanostructure, Hydrothermal, Solvothermal, Thermoelectric, Characterization, Lead Telluride, Bismuth Selenide, Skutterudites, Bi-Sb alloy, Thermal Conductivity

Date of Defense

3-18-2014

Abstract

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 200^ºC 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.

Identifier

FI14040858

Recommended Citation

Kadel, Kamal, "Synthesis and Characterization of Thermoelectric Nanomaterials" (2014). FIU Electronic Theses and Dissertations. 1170.
https://digitalcommons.fiu.edu/etd/1170