Date of Award

8-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Physics

Advisor

Tritt, Terry M

Committee Member

Daw , Murray S

Committee Member

Drymiotis , Fivos R

Committee Member

Ke , Pu-chun

Abstract

This dissertation focused on the investigation of the thermoelectric properties of PbTe nanocomposites, presenting a series of experimental investigation and qualitative theoretical analysis regarding utilizing the nanostructures to enhance the thermoelectrical properties. Three innovative synthesis techniques, which are related to fabricating nanocomposites, were developed. These three techniques are the size-selective growth of PbTe nanoparticles by a convection CVD technique, the nanolayer coating technique by hydrothermal method, and the alkali-metal-nano-surface-treatment. In the future, these techniques can be applied to many other thermoelectric material systems.

We proposed to use the grain boundary engineering technique route in the thermoelectric nanocomposite field and successfully applied this idea onto the PbTe nanocomposite fabrication. After two years of searching and experimenting, finally we developed a way to fabricate a stable and thermoelectrically favorable Te nanodot layer at the grain boundary using Na-hydrothermal treatment. This Te nanodot layer effectively allows the thermal conductivity to be appreciably lowered in the Pb0.75Sn0.25Te polycrystalline system. In the meantime, the electrical properties are largely preserved. Consequently, the thermoelectric figure of merit is considerably improved: ZT by ~ 40% and Z by ~ 57%. The presence of this Te nano-sized granular surface and its effects on thermal conductivity and electrical transport has given us an innovative new approach to achieving higher ZT values in other given TE materials.

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