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theses

Thermoelectric materials offer a potentially valuable source of energy by converting a temperature gradient to electricity. Recent progress in alloying, doping, and nanostructuring these materials has increased their figure of merit, bringing this technology closer to widespread use. However, the costs associated with processing and questions about fatigue reliability during long-term use could slow the development process. Liquid phase microstructure shapes are critical for sintering; further understanding of these shapes could potentially be used to improve mechanical response and lower overall processing costs. Here we review our progress with respect to the microstructure development of the material depending on heat treatment and composition. Thermoelectric materials made up of a PbTe/Ag2Te system were produced by heat treatments aimed at producing a liquid phase in the material. These samples were then examined through scanning electron microscopy, in an attempt to better understand the microstructure and track the liquid phase. This study was met with mixed results. While the process outlined does seem to produce faster sintering than undoped samples, full densification was not achieved. Furthermore, though the silver telluride was identified in the sample through the use of backscattering detection and EDS, the desired accuracy in finding the liquid phase was not achieved. However, the silver telluride was found to penetrate the grain boundaries, create secondary phases and form nano-precipitates, a development that is extremely promising as these features could all scatter phonons and raise the figure of merit of the material.    

ETD_5859

M.S.

Includes bibliographical references

by Sean McCoy Langan

doi:10.7282/T3542M8T

ETD graduate

The author owns the copyright to this work.