Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

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 200ºC 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

Share

COinS
 

Rights Statement

Rights Statement

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).