Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 110-113). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph.D.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on July 29, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Controls, Department of Electrical and Computer Engineering, University of Alberta. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Les matériaux tétraédrites de formule chimique [(Cu,Ag)10(Zn,Fe)2(Sb,As)4S13] sont des roches naturelles particulièrement abondantes sur Terre appartenant à la famille des sels sulfurés. Longtemps étudiées du point de vue structural et pour leur composition, ce n’est que récemment qu’ils ont suscité un intérêt pour la thermoélectricité en raison de leur très faible conductivité thermique. Afin d’étudier les performances de ces matériaux en terme de conversion d’énergie, les travaux de cette thèse ont consisté à les synthétiser par métallurgie des poudres puis à mesurer leurs propriétés thermoélectriques aussi bien à basse température (2 – 300 K) pour identifier les mécanismes microscopiques qui gouvernent les propriétés de transport qu’à haute température (300 – 700 K) pour déterminer leur domaine d’application optimal. L’étude de leur homogénéité chimique et de leur stabilité thermique a permis de confirmer l’existence d’une transition structurale pour certaines compositions menant à la séparation de phases lors du refroidissement, mécanisme connu en minéralogie et en géologie sous le terme d’exsolution. Celui-ci peut être responsable d’une modification des propriétés de transport et notamment d’une diminution de la conductivité thermique de l’ordre de 50%. De nombreuses substitutions ont été entreprises afin de tenter d’optimiser les performances de ces composés. Les matériaux tétraédrites présentent un caractère métallique qui évolue vers un état semi-conducteur selon la nature de l’élément en substitution et de sa concentration. D’autre part, une étude détaillée des propriétés thermiques de ces matériaux par diffusion inélastique des neutrons a permis de déterminer l’origine microscopique des très faibles valeurs de conductivité thermique observées dans ces matériaux / Tetrahedrite with general chemical formula [(Cu,Ag)10(Zn,Fe)2(Sb,As)4S13] are a family of natural minerals, widely spread on Earth, which belongs to the sulfosalt class of compounds. Discovered in the 19th century and extensively studied by mineralogists over the last 60 years from both structural and chemical points of view, it is not until recently however that they have focused attention in thermoelectricity due to their very low thermal conductivity. In order to study the performance of these materials in terms of energy conversion by thermoelectric effect, this thesis consisted in synthesizing tetrahedrite materials by powder metallurgy method and in determining their transport properties both at low (2-300 K) and high temperatures (300-700 K). This wide temperature range enabled us to identify the microscopic mechanisms that govern the transport properties and to assess their thermoelectric performances. The study of their chemical homogeneity and thermal stability has confirmed the existence of a structural transition for certain compositions leading to phase separation upon cooling, a mechanism known in mineralogy and geology as an exsolution process. This mechanism is responsible for a modification of the transport properties and especially an impressive decrease in the thermal conductivity of the order of 50%. Numerous substitutions have been undertaken in an attempt to optimize the thermoelectric performances of these compounds. Tetrahedrite materials exhibit a metallic character that evolves into a semiconductor state depending on the chemical nature of the substituting element and on its concentration. Moreover, a detailed study of the thermal properties of these materials by inelastic neutron scattering has unveiled the microscopic origin of the very low thermal conductivity values observed in these materials

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Temperature control is widely sought after in regards to optical systems as their optical parameters often show dependence on temperature. Examples include diode lasers, multiplexing systems, optical amplifiers, and filters all of whom have a high sensitivity to temperature. This thesis presents a temperature controlled environment chamber actuated by a thermoelectric cooler. The design of which provides a simple, multi-applicable solution for temperature control in optical devices. The final device is comprised of three sub-areas of design. Each subsystem was custom built and applied in the final assembly -- including a digitally implemented signal generator, an error correction controller, and the environment chamber heat sink structure. The signal generator is used as input for a switched-mode based Peltier driver found commercially. A feedback error controller compensates the driver for temperature control. Both systems are implemented with microcontroller units. The environment chamber heat sink assembly is designed specifically to handle the thermal energy generated by the thermoelectric cooler. All of the systems were tested collectively for functionality. The input signal generator achieved its design goals and is capable of creating specific profiles in the temperature response. Error controller performance was reasonable in set-point tracking for continuous input signals. Step input responses are tuned for minimal settling time and overshoot. Temperature resolution in the thermistor response is around 0.1•C after digital filtering. The thermal design achieved its goal of operating in an ambient environment up to 54°C. Low temperature ambient environment operation has been confirmed to 8°C. / Master of Science

The lead-free tin telluride (SnTe) is considered as a potential candidate to substitute lead telluride (PbTe) for thermoelectric power generation based on their similar crystal and electronic structures. However, the relatively high lattice thermal conductivity and low Seebeck coefficient of pristine SnTe are detrimental for real-life applications. This dissertation explored elements-doping/substituting of SnTe to overcome those shortcomings and improve SnTe thermoelectric performance. A series of the Sn1-xGexTe phases were synthesized and studied. When the Ge amount reaches 50% or higher, Sn1-xGexTe undergoes a phase transition from the rock-salt structure (Fm3̅m) to the rhombohedral one (R3m). The Sn0.5Ge0.5Te phase was explored in more details because it delivers the best thermoelectric performance with the Sn1-xGexTe series. The electron-richer Sb and Bi were substituted on the Sn/Ge site to optimize the charge transport properties, and Cu2Te was added into the matrix to improve the thermoelectric performance further. The In/Sb and In/Bi co-doping on the Sn/Ge sites was employed for Seebeck coefficient optimization. A comparative study of the electronic structure of the Sn0.5Ge0.5Te-based samples was performed. The calculations indicated a band convergence and changes in the valence band, thus providing insight into the co-doping effects. Suppression of the lattice thermal conductivity of SnTe was performed via alloying with AgSnSe2 and PbTe, which introduced strong atomic disorder. Additionally, AgSnSe2 showed a hole donor behavior in SnTe, and the increased carrier concentration compensated for the reduction in the carrier mobility, thus rendering a decent electrical conductivity in alloyed samples. As a result, the alloying effectively improved the samples' thermoelectric performance. / Thesis / Doctor of Philosophy (PhD) / In recent decades, renewable energy has attracted a lot of attention due to an increase in the global energy use and depletion of fossil fuel reserves. Thermoelectric materials are expected to play a vital role as green energy generators to overcome the upcoming energy crisis as they can directly convert waste heat into electricity through the Seebeck effect. In this dissertation, the main goal is optimizing the thermoelectric performance of SnTe for the above room temperature applications. Different doping/ substituting/alloying strategies were applied to improve the performance. The obtained thermoelectric properties of the SnTe-based materials were rationalized in terms of the charge carrier behavior, changes in the electronic structure, and phonon propagation.

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