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Les marchés de la thermoélectricité sont en pleine expansion avec l’intérêt croissant pour la récupération d’énergie thermique ou encore pour la gestion de la température de composants électroniques. En dépit de ses nombreux avantages, le développement de cette technologie est freiné par les performances des matériaux. Une voie d’amélioration identifiée est leur nanostructuration afin d’en diminuer la conductivité thermique de réseau.Dans ce travail de thèse, cette voie est appliquée au tellurure de bismuth, matériau connu pour posséder les meilleures performances autour de la température ambiante. Les matériaux sont obtenus par synthèse de nanoparticules en solution avant d’être mis en forme par pressage à chaud.Une première étude est réalisée sur la recherche d’un optimum de la taille de grain dans le massif. On montre que le contrôle des conditions de synthèse permet le contrôle des dimensions des nanoparticules. Par ailleurs, les analyses structurales et fonctionnelles des massifs après densification montrent que la variation de la taille initiale des particules permet le contrôle de la microstructure et des propriétés detransport des massifs.Une seconde étude porte sur la recherche d’un optimum en composition des matériaux Bi2Te3-xSex. Les analyses morphologiques mettent en évidence une structure complexe et particulière, laissant apparaitre la présence de trois phases dans les massifs.Les matériaux obtenus par cette méthode de synthèse possèdent a priori des propriétés de transport anisotropes. La caractérisation de leurs performances thermoélectriques est donc difficile. Plusieurs techniques de caractérisation sont mises en oeuvre afin de mieux connaitre leurs conductivités thermiques. Celles-ci sont faibles, ce qui montre l’intérêt de l’approche. Toutefois, leur conductivité électrique est plus basse que leurs homologues obtenus par des techniques plus conventionnelles. On montre néanmoins que l’optimisation des conditions de synthèse des particules entrant dans la composition des massifs alliés permet d’améliorer leurs propriétés électriques et donc leurs performances thermoélectriques / The global thermoelectric markets are in expansion with a growing interest for the energy harvesting or the thermal management of electronic components. Despite numerous advantages, this technology development is limited by the materials performances. A way to improve them is to use nanostructures in order to decrease the lattice thermal conductivity.In this work, this approach is applied to bismuth telluride, material well known for its high performance around room temperature. Materials are obtained from solution synthesis of nanoparticles before hot press compaction.A first study focuses on the determination of an optimal grain size in the bulk materials. It is shown that control over the synthesis parameters allows control on the size of nanoparticles.Moreover, structural and physical analyses on the bulks after sintering show that the change of thesynthesis parameters allows control over the microstructure and thermoelectric properties of the bulks.A second study is based on the study of an optimal composition of Bi2Te3-xSex materials. Morphological analysis show a specific and complex structure with three phases in the bulks.It is postulated that these materials should have anisotropic transport properties. Consequently, their characterizations are difficult. Different characterization techniques are used in order to have a better understanding of their thermal conductivities. Thermal conductivity of the bulks is found low which confirm the interest of this approach. However the electrical conductivity is lower than the one of the materials obtained by more conventional methods. We show that the synthesis parameters of the particles can be optimized to increase the thermoelectric performances of the bulk materials.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by James David Hodge. / Ph.D.

Neste trabalho desenvolvemos um estudo detalhado do processo de síntese e preparação de cristais de Bi IND 2 Te IND 3 e (Bi IND (l-x)Sb IND x) Te IND 3, bem como uma abordagem qualitativa sobre a variação do coeficiente Seebeck em função do comprimento destes cristais. Preparamos cristais com condutividade tipo-p e tipo-n pela técnica de Bridgman em um sistema com gradiente de temperatura axial fixo (29 °C/cm), e em outro em que este parâmetro poderia ser alterado facilmente. Os cristais de telureto de bismuto tipo-p preparados no primeiro equipamento foram axialmente homogêneos em composição e coeficiente Seebeck, cuja intensidade média medida foi de 220 V/K. Os tipo-n apresentaram uma fase rica em telúrio em todo o seu comprimento e uma diminuição gradativa do coeficiente Seebeck. O aparecimento desta fase pode ser associado à instabilidade da interface sólido-líquido ou a um processo de superresfriamento constitucional localizado. Por outro lado, em nenhum dos cristais de Bi IND 2 Te IND 3 e (Bi IND (l-x)Sb IND x) Te IND 3, com condutividade tipo-p e n preparados no segundo sistema, houve presença da fase rica em telúrio e o máximo valor do coeficiente Seebeck foi superior ao relatado na literatura. / ln this work, a detailed study on the synthesis and crystal growth process of Bi2Te3 e (Bi(l-x)Sbx)2 Te3 was carried out. The dependence of the Seebeck coefficient variation on the length crystal has been discussed in a qualitative way. P-type and n-type crystals were grown by the Bridgman technique using two different systems. In one system the axial temperature gradient was fixed, while in the other it could be adequately changed. The p-type bismuth tellurides grown in the first equipment were axially homogeneous in composition and Seebeck coefficient. Its average measured value was about 220 V/K. The n-type bismuth telluride presented a tellurium-rich phase in all of its extension and a decreasing Seebeck coefficient. The tellurium-rich phase can be related to solid-liquid interface instability or a constitucional supercooling. On the other hand, no Te-rich phase was detected in Bi2Te3 e (Bi(l-x)Sbx)2Te3 crystals grown in the second equipment. The maximum measured Seebeck coefficient of these materials was higher than the literature reported ones.

Neste trabalho desenvolvemos um estudo detalhado do processo de síntese e preparação de cristais de Bi IND 2 Te IND 3 e (Bi IND (l-x)Sb IND x) Te IND 3, bem como uma abordagem qualitativa sobre a variação do coeficiente Seebeck em função do comprimento destes cristais. Preparamos cristais com condutividade tipo-p e tipo-n pela técnica de Bridgman em um sistema com gradiente de temperatura axial fixo (29 °C/cm), e em outro em que este parâmetro poderia ser alterado facilmente. Os cristais de telureto de bismuto tipo-p preparados no primeiro equipamento foram axialmente homogêneos em composição e coeficiente Seebeck, cuja intensidade média medida foi de 220 V/K. Os tipo-n apresentaram uma fase rica em telúrio em todo o seu comprimento e uma diminuição gradativa do coeficiente Seebeck. O aparecimento desta fase pode ser associado à instabilidade da interface sólido-líquido ou a um processo de superresfriamento constitucional localizado. Por outro lado, em nenhum dos cristais de Bi IND 2 Te IND 3 e (Bi IND (l-x)Sb IND x) Te IND 3, com condutividade tipo-p e n preparados no segundo sistema, houve presença da fase rica em telúrio e o máximo valor do coeficiente Seebeck foi superior ao relatado na literatura. / ln this work, a detailed study on the synthesis and crystal growth process of Bi2Te3 e (Bi(l-x)Sbx)2 Te3 was carried out. The dependence of the Seebeck coefficient variation on the length crystal has been discussed in a qualitative way. P-type and n-type crystals were grown by the Bridgman technique using two different systems. In one system the axial temperature gradient was fixed, while in the other it could be adequately changed. The p-type bismuth tellurides grown in the first equipment were axially homogeneous in composition and Seebeck coefficient. Its average measured value was about 220 V/K. The n-type bismuth telluride presented a tellurium-rich phase in all of its extension and a decreasing Seebeck coefficient. The tellurium-rich phase can be related to solid-liquid interface instability or a constitucional supercooling. On the other hand, no Te-rich phase was detected in Bi2Te3 e (Bi(l-x)Sbx)2Te3 crystals grown in the second equipment. The maximum measured Seebeck coefficient of these materials was higher than the literature reported ones.

La creciente demanda de energía portátil requerida por sistemas miniaturizados está impulsando el desarrollo de nuevas tecnologías y materiales para lograr una eficiente generación de energía a una microescala. Los microgeneradores termoeléctricos ofrecen una oportunidad para recolectar el calor residual de dispositivos electrónicos y convertirlo en energía, eliminando a la vez dicho calor. La baja eficiencia de conversión termoeléctrica de los materiales semiconductores utilizados actualmente en microelectrónica ha limitado su aplicación para fines de aprovechamiento energético. Sin embargo, recientemente se ha constatado una mejora de varios órdenes de magnitud en las propiedades termoeléctricas del silicio cuando se presenta en forma de nanohilos, abriéndose de esta manera la oportunidad para la integración de generadores termoeléctricos en microtecnología de silicio. En esta tesis se han integrado monolíticamente matrices densas y ordenadas de nanohilos de silicio (Si NWs) en un dispositivo micromecanizado también en silicio. La técnica VLS-CVD ha sido utilizada para el crecimiento lateral controlado de los nanohilos. La microestructura ha sido apropiadamente diseñada para adaptar el crecimiento tridimensional de las matrices de nanohilos de silicio en una arquitectura plana y para asegurar el acceso eléctrico a los nanohilos. Adicionalmente, el dispositivo permite el establecimiento de un gradiente de temperatura interno plano cuando se pone en contacto con una fuente de calor, lo que da lugar a un microgenerador termoeléctrico completo en el que los nanohilos de silicio actúan como el material termoeléctrico nanoestructurado. Esta tesis tiene por objeto presentar los primeros desarrollos de integración de materiales termoeléctricos, técnicas de caracterización y tecnologías de fabricación realizados en el IMB-CNM (CSIC), sentando las bases para el desarrollo de futuras generaciones de microgeneradores termoeléctricos. Esta tesis se compone de cuatro capítulos. En el primer capítulo se presenta una breve introducción al mundo de la termoelectricidad, revisando el estado del arte de materiales y dispositivos termoeléctricos. El segundo capítulo está enfocado en las técnicas experimentales y tecnológicas empleadas a lo largo del estudio. El capítulo tres describe el proceso seguido para el diseño, simulación y fabricación de un microgenerador termoeléctrico plano basado en una sola matriz de nanohilos de silicio. Finalmente, el capítulo cuatro estudia el aumento en el rendimiento de los microgeneradoes termoeléctricos mediante matrices de nanohilos de silicio conectadas transversalmente, adaptando y explotando aún más el crecimiento lateral 3D de nanohilos de silicio VLS. / The increasing demand for portable power required by miniaturized systems is driving the development of new technologies and materials to achieve efficient energy generation at the microscale. Apart from removing heat from electronic devices, thermoelectric microgenerators offer an attractive opportunity to harvest waste heat converting it into power. The low thermoelectric conversion efficiency of current bulk microelectronics semiconductor materials has limited their implementation for energy harvesting purposes. However, recent studies have proven, at single nanowire level, that nanostructuring of silicon into nanowires greatly enhances the thermoelectric properties of this material, opening up the opportunity for the integration of thermoelectric generators into silicon microtechnology. In this thesis, dense and well-ordered arrays of silicon nanowires (Si NWs) have been monolithically integrated into a silicon micromachined device. The VLS-CVD technique has been used for the controlled lateral growth of nanowires. The microstructure has been appropriately designed to adapt the tridimensional growth of the Si NWs arrays to a planar architecture, and to assure electrical accessibility to the nanowires. Additionally, the device allows an internal in-plane temperature gradient to be established when placed in contact with a heat source, giving rise to a complete thermoelectric microgenerator in which the Si NWs act as the nanostructured thermoelectric material. This thesis is intended to bring new background in thermoelectric materials integration, characterization techniques and fabrication technologies to the IMB-CNM (CSIC), paving the way for the development of future generations of thermoelectric microgenerators. The work presented in this thesis is divided into four chapters. The first chapter introduces thermoelectricity and its underlying physics, reviewing the state-of-the-art of thermoelectric materials and devices. The second chapter focuses on the experimental and technological tools employed along this study. The third chapter describes the process followed for the design, simulation and fabrication of the building block of the proposed planar thermoelectric microgenerators based on a single Si NWs array. Finally, chapter four studies the enhanced performance of thermoelectric microgenerator structures by means of transversally linked Si NWs arrays, further adapting and exploiting the 3D lateral growth of VLS Si NWs.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 115-121).

Élaboration et caractérisation de composites hybrides thermoélectriques / Synthesis and characterisation of thermoelectric composites

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published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering