Dissertations / Theses on the topic 'Ceramic materials - Electric properties'
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Papageorge, Marc Vasilios. "Characterization of metal/ceramic interfaces on aluminum nitride." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9352.
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Kokan, Julie Runyan. "Microstructure/electrical property correlations in ceramic matrix composites." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19594.
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Yang, Fan. "Electrical and thermal properties of yttria-stabilised zirconia (YSZ)- based ceramic materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/electrical-and-thermal-properties-of-yttriastabilised-zirconia-ysz-based-ceramic-materials(82568afe-ffcb-4a38-9166-e5de83337763).html.
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Electrical and thermal conductivities of the yttria-stabilised zirconia/alumina (YSZ/Al2O3) composites and the yttria-zirconia-ceria (YSZ-CeO2) solid solutions are studied in this thesis. The electrical conductivity of the YSZ/Al2O3 composites decreases with an increase in the volume fraction of Al2O3 and exhibits typical percolation behaviour. The electrical conductivity of the YSZ/Al2O3 interface is higher than that of the YSZ grain boundary, but lower than that of the YSZ grains. The thermal conductivity of the YSZ/Al2O3 composites increases with an increase in the Al2O3 volume fraction, and it can be fitted well to the Maxwell theoretical model, which indicates the absence of obvious interfacial thermal resistances in the composites. The low interfacial thermal resistance of the YSZ/Al2O3 interface is due to the 'clean' and coherent nature of the YSZ/Al2O3 interface, along with the small difference between the elastic properties of YSZ and Al2O3. The electrical conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions has a 'V-shape' variation as a function of the mole ratio of CeO2 (x). In the ZrO2-rich region (x < 0.5), CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5), the increase of x increases the lattice parameter, which enlarges the free channel for oxygen vacancy migration. A comparison of the YSZ-CeO2 solid solutions with the YSZ-HfO2 series indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions.The thermal conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions also has a 'V-shape' variation as a function of the mole ratio of CeO2 (x), which indicates an incorporation of Zr4+ and Ce4+ can effectively decrease the thermal conductivity of the end members YSZ and yttria-doped ceria (YDC). In the ZrO2-rich region (0 ≤ x ≤ 0.5), the thermal conductivity is almost temperature independent; in the CeO2-rich region (0.5 ≤ x ≤ 1), it decreases obviously with increasing temperature. By calculating the phonon scattering coefficients, it is concluded that the composition dependence of the thermal conductivity in the ternary solid solutions is dominated by the mass difference between Zr and Ce at the cation sites, whereas the temperature dependence is determined by the order/disorder of oxygen vacancies at the anion sites.
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Mansour, Rabih. "Mode I Interlaminar Fracture Properties of Oxide and Non-Oxide Ceramic Matrix Composites." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1494248628194216.
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Darvish, Shadi. "Thermodynamic Investigation of La0.8Sr0.2MnO3±δ Cathode, including the Prediction of Defect Chemistry, Electrical Conductivity and Thermo-Mechanical Properties." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3653.
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Fundamental thermodynamic investigations have been carried out regarding the phase equilibria of La0.8Sr0.2MnO3±δ (LSM), a cathode of a solid oxide fuel cell (SOFC), utilizing the CALculation of PHAse Diagram (CALPHAD) approach. The assessed thermodynamic databases developed for LSM perovskite in contact with YSZ fluorite and the other species have been discussed. The application of computational thermodynamics to the cathode is comprehensively explained in detail, including the defect chemistry analysis as well as the quantitative Brouwer diagrams, electronic conductivity, cathode/electrolyte interface stability, thermomechanical properties of the cathode and the impact of gas impurities, such as CO2 as well as humidity, on the phase stability of the cathode. The quantitative Brouwer diagrams for LSM at different temperatures are developed and the detailed analysis of the Mn3+ charge disproportionation behavior and the electronic conductivity in the temperature range of 1000-1200°C revealed a good agreement with the available experimental observations. The effects of temperature, CO2 partial pressure, O2 partial pressure, humidity level and the cathode composition on the formation of secondary phases have been investigated and correlated with the available experimental results found in the literature. It has been indicated that the CO2 exposure does not change the electronic/ionic carriers’ concentration in the perovskite phase. The observed electrical conductivity drop is predicted to occur due to the formation of secondary phases such as LaZr2O7, SrZrO3, SrCO3 and Mn oxides at the LSM/YSZ interface, resulting in the blocking of the electron/ion transfer paths. For the thermo-mechanical properties of LSM, a new weight loss Mechanism for (La0.8Sr0.2)0.98MnO3±δ using the La-Sr-Mn-O thermodynamic database is modeled with respect to the compound energy formalism model. This newly proposed mechanism comprehensively explains the defect formation as a result of volume/weight change during the thermal cycles. According to the proposed mechanism the impact of cation vacancies regarding the volume change of cathode was explained.
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Wagner, Michael Christopher. "An Investigation of the Optical and Physical Properties of Lead Magnesium Niobate-Lead Titanate Ceramic." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1608306745644145.
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Almansour, Amjad Saleh Ali. "USE OF SINGLE TOW CERAMIC MATRIX MINICOMPOSITES TO DETERMINE FUNDAMENTAL ROOM AND ELEVATED TEMPERATURE PROPERTIES." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron148640184494135.
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SILVA, PAULO S. M. da. "Projeto, construção e testes de um sistema de medidas elétricas e estudo de compósitos de zircônia-ítria e nitreto de titânio." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/25318.
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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Zapata, Angélica Maria Mazuera. "Processamento e propriedades do sistema ferroelétrico (Li,K,Na)(Nb,Ta)O3 dopado com CuO." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/5071.
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Previous issue date: 2015-03-09Financiadora de Estudos e Projetos
The search for new lead-free piezoelectric materials has been a major goal of many scientists in recent years. The main cause is the replacement of widely used lead zirconate titanate (PZT) based ceramics due to the highly toxic characteristics of the lead element. Potassium sodium niobate based ceramics have shown high piezoelectric coefficients and a morphotropic phase boundary close to the composition (K0.5Na0.5)NbO3 (KNN), similar to that found in lead zirconate titanate. However, the preparation of highly dense KNN based ceramics is extremely difficult. In this work, the structural, mechanical and electrical properties of lead free ferroelectric ceramics with compositions Li0,03(K0,5Na0,5)0,97Nb0,8Ta0,2O3 + xwt% CuO (x = 0; 2 and 3.5) were studied. All the compositions, sintered at 1050ºC for 2 hours had high density, approximately 95% of the theoretical value. Rietveld refinement of the X ray diffraction patterns showed a mixture of both orthorhombic Bmm2 and tetragonal P4mm phases, for all compositions. Nevertheless, compositions with high CuO contents have mainly the tetragonal phase. Dielectric and dynamic mechanical analysis (DMA) measurements showed two polymorphic phase transitions with increasing temperature. Both phase transitions have diffuse character and they can be related with the transformation of the orthorhombic phase fraction in the tetragonal one, and with the transformation of the tetragonal ferroelectric phase to a cubic paraelectric one. The origin of the difference observed between the temperatures where both techniques, dielectric and mechanical, see the diffuse phase transition is discussed. The ceramic with 2wt% of CuO is electrically softer than the other compositions and it has the highest value of the piezoelectric coefficient d31. Also, in this work we studied the possibility of using high contents of CuO to promote the formation of liquid phase for obtaining and extracting single crystal seeds, which can be used for the texture of KNN-based ceramics. The ceramic Li0,03(Na0,5K0,5)0,97Ta0,2Nb0,8O3 + x wt% CuO with x=16, sintered at 1090ºC for 2 hours, is a perfect candidate for extracting grains which may be used as seeds. Furthermore, ceramics with x=13, sintered at 1110ºC for 2 hours, showed a partial melting of the material, which caused the growth of highly oriented grains. This material can be practically considered as a single crystal and, with a proper cut procedure, the desired single crystal seeds can be obtained. This method to obtain single crystal seeds, as proposed in this work, is very simple and novelty.
Nos últimos anos, o foco principal de muitos cientistas tem sido a procura de novos materiais piezoelétricos livres de chumbo. A causa principal é a substituição dos materiais baseados em titanato zirconato de chumbo (PZT), os quais são amplamente utilizados em aplicações piezoelétricas, devido à alta toxicidade do elemento chumbo. Cerâmicas baseadas em niobato de sódio e potássio têm mostrado altos coeficientes piezoelétricos e um contorno de fases morfotrópico próximo da composição (K0.5Na0.5)NbO3 (KNN), similar ao encontrado no titanato zirconato de chumbo. Porém, a preparação de cerâmicas baseadas em KNN com alta densidade é extremamente dificultosa. Neste trabalho foram estudadas as propriedades estruturais, mecânicas e elétricas de cerâmicas ferroelétricas livres de chumbo com composições Li0,03(K0,5Na0,5)0,97Nb0,8Ta0,2O3 + x %P CuO (x = 0; 2 e 3,5). Todas as cerâmicas sinterizadas a 1050ºC durante 2 horas apresentaram altas densidades, sendo aproximadamente 95% da densidade teórica. O refinamento pelo método de Rietveld dos perfis de difração de raios X mostrou que todas as composições apresentam uma mistura de ambas as fases, ortorrômbica Bmm2 e tetragonal P4mm. Porém, composições com altos teores de CuO apresentam a fase tetragonal como sendo majoritária. As medidas dielétricas e as de análise mecânico dinâmico (DMA) mostraram duas transições de fase polimórficas com o aumento da temperatura. Ambas transições de fase têm caráter difuso e estão relacionadas com a transformação da fração de fase ortorrômbica em tetragonal e com a transformação da fase tetragonal ferroelétrica para cúbica paraelétrica. Foi discutida a origem da diferença observada, nas temperaturas em que ambas as técnicas, dielétrica e mecânica, enxergam a transição de fase difusa. A cerâmica com 2%P de CuO mostrou-se mais mole eletricamente e apresentou um valor maior de coeficiente piezoelétrico d31 do que as outras composições estudadas. Também, neste trabalho foi estudada a possibilidade de usar altos teores de CuO para promover a formação de fase líquida e conseguir a formação e extração de sementes monocristalinas que possam ser utilizadas na textura de cerâmicas baseadas em KNN. A cerâmica de Li0,03(Na0,5K0,5)0,97Ta0,2Nb0,8O3 + x % P CuO com x=16, sinterizada a 1090ºC durante 2 horas, mostrou-se a candidata perfeita para a extração de grãos que possam ser utilizados como sementes. Por outro lado, a cerâmica com x=13, sinterizada a 1110ºC durante 2 horas, apresentou fusão parcial de material, o que promoveu o crescimento dos grãos altamente orientados de forma que esse material já pode ser considerado como sendo praticamente um monocristal e com um procedimento de corte adequado, podem ser obtidas as sementes monocristalinas desejadas. Esse procedimento de obtenção de sementes monocristalinas, proposto neste trabalho, é totalmente simples e inovador.
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COSTA, FRANCINE A. da. "Sintese e sinterizacao de pos compositos do sistema W-Cu." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11176.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:00/00255-9
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Saunders, Theo Graves. "Effect of electric current on ceramic processing." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25943.
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This work was on the effect of electric current on the processing of ceramics. The focus was on electromigration/electrochemistry and plasma effects. While there is no solid evidence that there is plasma in Spark Plasma Sintering, (SPS), newer techniques e.g. flash, use different conditions so there is an interest in understanding the conditions under which a plasma forms. The minimum arcing voltage was found from literature to be from 10-15V for materials of interest. This is above that found in SPS (10V). However, due to the many contact points in a powder compact much higher voltages (50V) were required in practical experiments. Optical spectroscopy was used to verify the formation of a plasma, and emission peaks from the powder compact material were visible implying they were vaporised and formed the plasma. Electromigration was exploited to alter the oxidation of zirconium diboride, by passing current through the oxide layer (120μm zirconia base grown at 1200°C) oxygen could be pumped either away or toward the diboride bulk. Small cubes (3mm) of diboride had platinum foil electrodes applied on both sides and oxidation was performed at 1400°C for 5hr. Without a field the oxide grew to 360μm, by applying 10V and 100mA the oxide grew to 150μm under the +ve electrode but 1400μm under the -ve electrode. Electrochemical reduction was believed to have occurred due to the electrical properties of the material changing during oxidation and visible blackening of the oxide. Combining the techniques from both earlier works, a contactless flash sintering setup was developed. This used two plasma arcs as electrodes to heat and pass current through the sample. Various materials, currents and times were used, but the best result was with SiC:B4C which was sintered in 3s with 6A, the microstructure showed sharp grains, no segregation and limited grain growth ( initially 0.7μm SiC and 0.5μm B4C, this grew to 1.1μm and 1.4μm). This was the first recorded case of contactless flash sintering and the technique has the potential to sinter ceramics in a continuous manner.
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Bera, Chandan. "Thermo electric properties of nanocomposite materials." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00576360.
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Cette thèse présente une étude théorique du transport de chaleur dans les matériaux composites nano poreux et nano fils ainsi qu'une étude théorique des propriétés thermoélectriques de l'alliage Si0:8Ge0:2 confrontée à des mesures expérimentales réalisées pour une partie, dans le cadre de l'étude.La première étude démontre que les alliages poreux affichent des réductions de conductivité thermique à des dimensions de pores beaucoup plus grandes que les matériaux poreux non alliés de même porosité nominale. Si on considère une taille de pores de 1000nm, la conductivité thermique de l'alliage Si0:5Ge0:5 avec 0:1 de porosité est deux fois plus faible que la conductivité thermique d'un matériau non poreux, alors que les pores plus petits que 100 nm sont nécessaires pour obtenir la même réduction relative dans le Si ou Ge pur. Nos résultats indiquent que les alliages nano poreux devraient être avantageux devant les matériaux nano poreux non alliés, et ceux pour les applications nécessitant une faible conductivité thermique, tels que les nouveaux matériaux thermoélectriques.La deuxième étude théorique sur la conductance thermique de nano fils révèle l'effet de la structure sur le transport des phonons. Avec un modèle théorique qui considère la dépendance en fréquence du transport des phonons, nous sommes en mesure quantitativement de rendre compte des résultats expérimentaux sur des nano fils droits et coudés dans la gamme de température qui montre qu'un double coude sur un fil réduit sa conductance thermique de 40% à la température de 5K. Enfin, nous avons procédé à une approche théorique des propriétés thermoélectriques des alliages SiGe frittés, en les comparant aux mesures expérimentales nouvelles et antérieures, tout en évaluant leur potentiel d'amélioration. L'approche théorique a été validée par comparaison de la mobilité prévue et la conductivité thermique prévues, en faisant varier la quantité de Ge et les concentrations de dopage, dans une gamme de température comprise entre 300 et 1000K. Nos calculs suggèrent qu'une optimisation par rapport à l'état de l'art actuel est possible pour le matériau de type n et type p, conduisant potentiellement à une augmentation de 6% (5%) du ZT _a 1000K et 25% (4%) _a température ambiante. Même des améliorations plus grandes devraient être possibles si la probabilité de diffusion des phonons aux joints de grains pouvait être augmentée au-delà de sa valeur actuelle de 10%.
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Andersson, David. "From the Electronic Structure of Point Defects to Functional Properties of Metals and Ceramics." Doctoral thesis, Stockholm : Materialvetenskap, Materials Science and Engineering, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4309.
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SENE, FRANK F. "Resistividade eletrica de materiais compositos do tipo ceramica-metal na regiao de percolacao: aplicacao em cadinhos para fornos de inducao." reponame:Repositório Institucional do IPEN, 1997. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10657.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Yeomans, J. A. "Ceramic tool materials : structure and properties relevant to wear." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233360.
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This thesis is concerned with the microstructures and wear characteristics of eight ceramic tool materials which have been, or are currently, commercially available as indexable inserts for lathe tools. Two of the materials are alumina-based and the other six are derived from silicon nitride. The opening chapters of the thesis outline the essential features of metal cutting, the properties required of a good tool material, the development of ceramic tools and possible wear behaviour as discussed in the literature. Subsequent chapters describe the experimental procedures adopted in this work and both present and discuss the results obtained. The eight ceramics have been microstructurally characterised by the use of X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. Machining tests have been performed using five common workpiece materials, spanning a range of nickel and iron contents: mild steel, stainless steel, two nickel-based superalloys and commercial purity nickel. The two alumina-based materials were found to wear in a different, less severe manner to the silicon nitride-based tools. The mechanical response to surface contacts was established using identation techniques to give hardness (as a function of contact size and temperature) and fracture toughness (as a function of temperature) to test the correlation between these properties and wear behaviour, but this proved to be unfruitful. Since other classes of tools can be subject to dissolution/diffusion wear and little is known about the compatability of these ceramics with molten metals, a second type of investigation was instigated. The involved immersing pieces of ceramic in samples of molten workpiece materials, followed by cooling, sectioning and examining in the scanning electron microscope. Vast differences in the behaviour of the materials were observed and results from these tests correlated well with machining data, indicating the importance of high temperature stability with respect to the hot workpiece. Drawing on the experimental observations made during the project, the thesis concludes with suggestions for improving and optimising ceramic tool materials for turning purposes.
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Simmons, Jed. "OPTICAL AND PHYSICAL PROPERTIES OF CERAMIC CRYSTAL LASER MATERIALS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4123.
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Historically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic crystal using an interferometric method. The interferometer employed a spatially filtered HeNe at 633 nm wavelength. Thermal expansion coefficients measured for the ceramic crystal samples were near the reported values for single crystal Nd:YAG. With a similar experimental setup as that for the thermal expansion measurements, dn/dT for ceramic crystal Nd:YAG was measured and found to be slightly higher than the reported value for single crystal. Depolarization loss due to thermal gradient induced stresses can limit laser performance. As a result this phenomenon was modeled for ceramic crystal materials and compared to single crystals for slab and rod shaped gain media. This was accomplished using COMSOL Multiphysics, and MATLAB. Results indicate a dependence of the depolarization loss on the grain size where the loss decreases with decreased grain size even to the point where lower loss may be expected in ceramic crystals than in single crystal samples when the grain sizes in the ceramic crystal are sufficiently small. Deformation-induced thermal lensing was modeled for a single crystal slab and its relevance to ceramic crystal is discussed. Data indicates the most notable cause of deformation-induced thermal lensing is a consequence of the deformation of the top and bottom surfaces. Also, the strength of the lensing along the thickness is greater than the width and greater than that due to other causes of lensing along the thickness of the slab. Emission spectra, absorption spectra, and fluorescence lifetime were measured for Nd:YAG ceramic crystal and Yb:Lu2O3 ceramic crystal. No apparent inhomogeneous broadening appears to exist in the Nd:YAG ceramic at low concentrations. Concentration and temperature dependence effects on emission spectra were measured and are presented. Laser action in a thin disk of Yb:Y2O3 ceramic crystal was achieved. Pumping was accomplished with a fiber coupled diode laser stack at 938 nm. A slope efficiency of 34% was achieved with maximum output energy of 28.8 mJ/pulse.Ph.D.
Department of Physics
Sciences
Physics PhD
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Misra, Rajnish. "Controlled drying to enhance properties of technical ceramic materials." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366120.
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Rickles, Stacey A. "Microstructural and compressive properties of a metal/ceramic syntactic foam." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19677.
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Ben, Kaabar Aymen. "Durabilité des assemblages céramique-métal employés en électronique de puissance." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0064/document.
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Les composants d’électronique de puissance ont (et vont encore avoir !) eu une grande influence sur les secteurs de l'énergie et des transports. Ces pièces sont notamment constitués d’assemblages céramique –cuivre pour lesquels la tenue mécanique doit être maîtrisée afin de garantir dans le future une durabilité d’environ 30 ans sous l’action de cycles thermiques plus en plus grande. Une analyse des mécanismes de défaillance des assemblages DBC (Direct Bonding Copper) utilisés en électronique de puissance est étudiée (le délaminage le long de l’interface cuivre -céramique et/ou la rupture fragile de la céramique). Pour identifier le comportement élastoplastique du cuivre, nous avons montré qu’il est nécessaire d’utiliser une plaque de cuivre ayant subi l’ensemble des traitements thermiques liés au processus d’assemblage. Le comportement élastique fragile de la céramique est décrite dans le cadre d’une statistique de Weibull. Dès lors, une caractérisation du délaminage cuivre-céramique sous flexion quatre points a permis d’identifier un modèle cohésif pour l’interface. La calibration des paramètres cohésifs est menée en utilisant les données à deux échelles : i) macroscopique de force-déplacement ii) locale de suivi optique de la fissuration avec le déplacement imposé. L’intégrité mécanique des assemblages DBC pour différentes épaisseurs des couches de cuivre et de céramique a été étudié. Nous avons montré que les configurations avec un rapport proche de l’unité sont les plus dangereuses en engendrant un délaminage, qui se poursuit sous cyclage thermique. Ce dernier peut être notablement réduit en structurant le pourtour de la surface de cuivre avec des trous cylindriques répartis périodiquement. Ainsi, un modèle éléments finis permettant d’évaluer les assemblages les plus prometteurs en terme de durabilité a été établie. En l’absence de défauts géométrique, la couche de cuivre reste intègre, même dans le cas d’un délaminage dont le front induit une concentration de contrainteThe power electronics components (and still will have!) have a great influence on the energy and transport sectors. These parts are made of ceramic-copper assemblies for which the mechanical strength must be controlled to ensure durability about 30 years under the thermal cycles increasingly larger. A failure mechanisms analysis in DBC (Direct Copper Bonding) assemblies used in power electronics is studied (the delamination along the interface copper - ceramic and/or the brittle ceramic fracture). To identify the elastoplastic behavior of copper, we showed that it’s necessary to use a copper plate having undergone the heat hole treatments related to the assembly process. The ceramic gragile elastic behavior is descrobed within the Weibull statictics framework. Consequently, a copper-ceramic delamination characterization under four points bending made it possible to identify a cohesive model for the interface. The cohesive calibration parameters is carried out by using the data in two scales: i) strentgh-displacement macroscopic ii) local cracking optical follow-up with imposed displacement. The mechanical integrity of DBC assemblies of different thickness of copper and ceramic has been studied. We showed that the configurations with a ratio close to the unit are most dangerous by generating a delamination, which continues under thermal cycling. This risk of delamination can be notably reduced by structuring the copper circumference surface with cylindrical holes distributed periodically. Thus, a finite elements model allowing us to evaluate the most promising assemblies in term of durability, was estabilshed. In the absence of geometrical defects, the copper layer must remains, even in the delamination case whose face induces a concentration stress
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Dunyak, Thomas John. "Properties and performance of a ceramic composite component." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134634/.
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Grande, Dodd Harrison. "Testing and properties of high temperature glass-ceramic matrix composites." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14952.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 109-118.
by Dodd Harrison Grande.
Ph.D.
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Zahedi, Maryam. "Meshfree Method for Prediction of Thermal Properties of Porous Ceramic Materials." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/954.
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In the presented thesis work, meshfree method with distance fields is applied to create a novel computational approach which enables inclusion of the realistic geometric models of the microstructure and liberates Finite Element Analysis(FEA) from thedependance on and limitations of meshing of fine microstructural feature such as splats and porosity.Manufacturing processes of ceramics produce materials with complex porosity microstructure.Geometry of pores, their size and location substantially affect macro scale physical properties of the material. Complex structure and geometry of the pores severely limit application of modern Finite Element Analysis methods because they require construction of spatial grids (meshes) that conform to the geometric shape of the structure. As a result, there are virtually no effective tools available for predicting overall mechanical and thermal properties of porous materials based on their microstructure. This thesis is a separate handling and controls of geometric and physical computational models that are seamlessly combined at solution run time. Using the proposedapproach we will determine the effective thermal conductivity tensor of real porous ceramic materials featuring both isotropic and anisotropic thermal properties. This work involved development and implementation of numerical algorithms, data structure, and software.
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English, Jennifer M. "Wireless micromachined ceramic pressure sensors for high termperature environments." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/15790.
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Porwal, Harshit. "Processing and properties of graphene reinforced glass/ceramic composites." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9107.
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This research provides a comprehensive investigation in understanding the effect of the addition of graphene nano-platelets (GNP) on the mechanical, tribological and biological properties of glass/ceramic composites. We investigated two kinds of materials namely amorphous matrices like glasses (silica, bioglass) and polycrystalline matrices like ceramics (alumina). The idea was to understand the effect of GNP on these matrices as GNP was expected to behave differently in these composites. Bioglass (BG) was also chosen as a matrix material to prepare BG-GNP composites. GNP can improve the electrical conductivity of BG which can be used further for bone tissue engineering applications. The effect of GNP on both electrical conductivity and bio-activity of BG-GNP composites was investigated in detail. There were three main problems for fabricating these novel nano-composites: 1) Production of good quality graphene; 2) Homogeneous dispersion of graphene in a glass/ceramic matrix and; 3) Retention of the graphitic structure during high temperature processing. The first problem was solved by synthesising GNP using liquid phase exfoliation method instead of using a commercially available GNP. The prepared GNP were ~1 μm in length with a thickness of 3-4 layers confirmed using transmission electron microscopy. In order to solve the second problem various processing techniques were used including powder and colloidal processing routes along with different solvents. Processing parameters were optimised to fabricate glass/ceramic-GNP composite powders. Finally in order to avoid thermal degradation of the GNP during high temperature processing composites were sintered using spark plasma sintering (SPS) technique. Fully dense composites were obtained without damaging GNP during the sintering process also confirmed via Raman spectroscopy. Finally the prepared composites were characterised for mechanical, tribological and biological applications. Interestingly fracture toughness and wear resistance of the silica nano-composites increased with increasing concentration of GNP in the glass matrix. There was an improvement of ~45% in the fracture toughness and ~550% in the wear resistance of silica-GNP composites with the addition of 5 vol% GNP. GNP was found to be aligned in a direction perpendicular to the applied force in SPS. In contrast to amorphous materials fracture toughness and scratch resistance of alumina-GNP composites increased only for small loading of GNP and properties of the composites decreased after a critical concentration. There was an improvement of ~40% in the fracture toughness with the addition of only 0.5 vol% GNP in the alumina matrix while the scratch resistance of the composite increased by ~10% in the micro-ductile region. Electrical conductivity of the BG-GNP composite was increased by ~9 orders of magnitude compared to pure BG. In vitro bioactivity tests performed on BG-GNP composites confirmed that the addition of GNP to BG matrix also improved the bioactivity of the nano-composites confirmed using XRD analysis. Future work should focus on understanding electrical and thermal properties of these novel nano-composites.
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Namjoshi, Shanatanu Ashok. "Reaction synthesis of dynamically-densified Ti-based intermetallic and ceramic forming powders." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19572.
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McClorey, Catherine. "Compositional and mechanical properties of polymer/ceramic composite materials for medical applications." Thesis, University of Ulster, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369954.
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Jantunen, H. (Heli). "A novel Low Temperature Co-firing Ceramic (LTCC) material for telecommunication devices." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:951426553X.
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Abstract
The thesis describes the development of a novel LTCC material system for RF and
microwave telecommunication purposes.
The work has been divided into three parts. In the first section, the
compositional and firing properties of this novel LTCC dielectric have been
studied as well as its thermomechanical and dielectric properties. The second
section describes the multilayer component preparation procedure for the ceramic
material including tape casting and lamination parameters and the selection of
the conductor paste. In the last section, the novel LTCC material system has been
used to demonstrate its properties in RF multilayer resonators and a bandpass
filter.
The dielectric material for the novel LTCC system was prepared using magnesium
calcium titanate ceramic, the firing temperature of which was decreased to
900°C
by the addition of a mixture of zinc oxide, silicon oxide and boron oxide. The
powder was made without any prior glass preparation, which is an important
process advantage of this composition. The fired microstructure was totally
crystalline with high density (3.7 Mg m-3) and low
porosity (0.5 %). The mechanical properties were virtually identical to the values of the commercial
LTCCs, but the higher thermal expansivity makes it most compatible with alumina
substrates. The dielectric values were also good. The permittivity was 8.5 and
the dissipation factor (0.9·10-3 at 8 GHz) less
than that of the commercial
LTCCs. Furthermore, the temperature coefficient of the resonance frequency was
demonstrated to be adjustable between the range of +8.8 ... -62 ppm/K with a
simple compositional variation of titanium oxide.
The slurry for the tape casting was prepared using poly(vinyl butyral) -base
organic additives and the 110 μm thick tapes had a smooth surface (RA < 0.5
μm).
The multilayer components were prepared using 20 MPa lamination pressure,
90°C
temperature and 1 h dwell time. The most suitable conductor paste for this
composition was found to be commercial silver paste (duPont 6160), which produced
satisfactory inner and outer conductor patterns for multilayer components.
Finally, resonators with a resonant frequency range of 1.7 ... 3.7 GHz were
prepared together with a bandpass filter suitable for the next generation of
telecommunication devices. This demonstration showed the potential of the
developed novel LTCC material system at high RF frequencies.
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Duchez, Wilfried. "Role of electric field profiles in continuous microwave processing of thermal runaway materials." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02132009-171150/.
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Tepesch, Patrick David. "Atomistic modeling of ceramic materials : predicting crystal structures, thermodynamic properties, and diffusion behavior." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10936.
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Park, Jun-Young. "Solid-state electrochemical properties of oxygen-ion conducting ceramic materials and their applications." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006660.
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Akinyeye, Richard Odunayo. "Nanostructured polypyrrole impedimetric sensors for anthropogenic organic pollutants." Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5301_1248150815.
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The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.
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Stackpoole, Margaret Mary. "Reactive processing and mechanical properties of polymer derived silicon nitride matrix composites and their use in coating and joining ceramics and ceramic matrix composites /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10564.
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Carney, Alison Fox. "The effect of microstructure on the mechanical properties of a 30% titanium diboride/70% alumina composite." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19994.
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Milsom, Ben. "The effect of CNTs on the sintering behaviour and properties of structural ceramic composites." Thesis, Queen Mary, University of London, 2013. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8367.
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This research provides a comprehensive investigation into the effects of carbon nanotubes (CNTs) on the sintering behaviour, grain growth and properties of ceramics. Contradictory results reported in the literature on the effect of CNTs on sintering behaviour indicated the need for a systematic investigation under reproducible, controllable conditions. The sintering studies were performed using instrumented spark plasma sintering (SPS). It is a rapid sintering process that allows sintering to be studied in real time under isothermal conditions, enabling accurate calculation of time exponents and activation energies. A study into the effects of CNTs on the sintering behaviour of PSZ and B4C has shown that the presence of CNT content above the percolation threshold significantly reduces the sintering activation energies by 62 and 38% respectively. In both systems, the CNTS were also found to enhance the grain boundary diffusion mechanism of consolidation. Below the percolation threshold there was no significant effect on the activation energy. As well as the sintering behaviour, the grain growth of the PSZ and PSZ CNT composites was investigated. This research found that the CNTs acted as a grain growth inhibitor through a solute drag like mechanism both below and above the percolation threshold although with a high CNT content the solute drag effect was enhanced further with no significant change to the activation energy. The degradation of the CNTs was examined to determine whether they maintain their structural integrity during sintering. It was found that in both matrices with increasing temperature the CNTs were degraded to a greater extent. In the case of the PSZ-CNT composite the degradation was measured with respect to time at a series of temperatures to investigate the mechanism of degradation. Abstract ii The thermal properties of the ceramic CNT composites and porous ceramics were examined to determine the effect of CNTs on the transport properties of the matrix. It was found that the inclusion of CNTs in a PSZ matrix could enhance the thermal diffusivity and the residual porosity caused by burning them out causes a reduction.
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Zhao, Yilin [Verfasser]. "Thermo-mechanical properties of glass-ceramic solid oxide fuel cell sealant materials / Yilin Zhao." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1046975137/34.
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Rastkar, Siavash. "Characterization of Homogenized Mechanical Properties of Porous Ceramic Materials Based on Their Realistic Microstructure." FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2478.
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The recent advances in the Materials Engineering have led to the development of new materials with customized microstructure in which the properties of its constituents and their geometric distribution have a considerable effect on determination of the macroscopic properties of the substance. Direct inclusion of the material microstructure in the analysis on a macro level is challenging since spatial meshes created for the analysis should have enough resolution to be able to accurately capture the geometry of the microstructure. In most cases this leads to a huge finite element model which requires a substantial amount of computational resources.
To circumvent this limitation a number of homogenization techniques were developed. By considering a small element of the material, referred to as Representative Volume Element (RVE), homogenization methods make it possible to include the effects of a material’s microstructure on the overall properties at the macro level. However, complexity of the microstructure geometry and the necessity of satisfying periodic boundary conditions introduce additional difficulties into the analysis procedure.
In this dissertation we propose a hybrid homogenization method that combines Asymptotic homogenization with MeshFree Solution Structures Method (SSM). Our approach allows realistic inclusion of complex geometry of the microstructure that can be captured from micrographs or micro CT scans. In addition to unprecedented flexibility in handling complex geometries, this method also provides a completely automatic analysis procedure. Using meshfree solution structures simplifies meshing to creating a simple cartesian grid which only needs to contain the domain. This also eliminates manual modifications which usually needs to be performed on meshes created from image data.
A computational platform is developed in C++ based on meshfree/asymptotic method. In this platform also a novel meshfree solution structure is designed to provide exact satisfaction of periodic boundary conditions for boundary value problems such as homogenization. Performance of the developed platform is tested over 2D and 3D domains against previously published data and/or conventional finite element methods. After getting satisfactory results, homogenized properties are used to compute localized stress and strain distributions over inhomogeneous structures.
Furthermore, effects of geometric features of pores/inclusions on homogenized mechanical properties is investigated and it is demonstrated that the developed platform could provide an automated quantitative analysis tool for studying effects of different design parameters on homogenized properties.
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俞佩賢 and Pui-yin Yu. "Metal alkylidyne complexes as building blocks for molecular materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31238002.
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COSTA, GUSTAVO C. C. da. "Sintese, caracterizacao estrutural, termoquimica e eletrica de materiais ceramicos para celulas a combustivel de oxido solido." reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11784.
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Made available in DSpace on 2014-10-09T12:55:47Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:05:19Z (GMT). No. of bitstreams: 0
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:05/54171-4
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Humbert, William R. "A new technique for measuring the elctromagnetic properties of rotationally symmetric materials." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/14941.
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Furlong, Scott Davis. "Reduction of radiated thermal conductivity in thin-wall hollow ceramic spheres using scattering phases." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/9341.
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Sirman, John Derrick. "A study of the mass transport and electrochemical properties of materials for ceramic oxygen generators." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/11279.
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Thomsen, Elizabeth Alice. "Characterisation of materials for organic photovoltaics." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/462.
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Tanikella, Ravindra V. "Variable frequency microwave processing of materials for microelectronic applications." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/10271.
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Wang, Dashan 1948. "Thermal stability of SrFeO3SiO2Si and SrFeO3AI2O3 thin film systems : transmission electron microscopy study of interfacial structures of the thin film systems and conductometric sensing response of SrFeO3AI2O3." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115907.
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The literature review indicates that studies on the structures and properties of perovskites materials have shown attractive applications in the fields of energy, catalysts and sensing materials for fuel cell and sensing industries. Kinetic phenomena in thin film systems, such as solid state amorphization and interface reactions due to diffusion during thin film deposition, are introduced indicating that thermal stability is a concern in thin film sensor device application. The principle of traditional methods of materials characterization is briefly discussed. Emphasis is placed on the functions of analytical transmission electron microscopy.The SrFeO3/SiO2/Si and SrFeO3/Al 2O3 thin film systems have been studied using transmission electron microscopy. The thin films of SrFeO3 were grown by pulsed laser deposition. For the SrFeO3/SiO2/Si system, TEM characterization showed that the microstructure of the film deposited at room temperature contained crystalline and amorphous layers. Silicon diffusion into SrFeO3 films occurred at the SiO2 interface. The silicon-induced interfacial reactions resulted in phase transformations and the growth of complex crystalline and amorphous phases. The principal compositions of these phases were Sr(Fe,Si)12O19, SrOx and amorphous [Sr-Fe-Si-O].
The films in the SrFeO3/Al2O3 system were deposited onto single crystal and sintered polycrystalline Al2O 3 substrates at room temperature and 700°C and subjected to annealing for various periods of time at 700-1000°C. TEM characterization showed that the morphology of the film varied with changes in deposition temperature: a columnar structure was produced at room temperature and layers containing crystalline grains were produced at 700°C. The interfacial structures of the films remained unchanged below 700°C. Interfacial reactions were observed following annealing at 850°C for 5 hours. The phase transformation at the interface was characterized for the film annealed at 1000°C for 5 hours, for which the principal phases were identified as SrAl2-xFe xO4 and SrFe12-yAlyO19. As a result, an isothermal section at 1000°C of a ternary phase diagram for SrO-Al2O3-Fe2O3 is proposed. Evaluation for thin film conductometric sensing applications indicated that the untreated films deposited at 700°C onto both single crystal and sintered Al2O3 substrates exhibited a similar temperature dependency of conductivity in air and a p-type gas sensor response to oxygen and propane at 500°C.
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Wells, Andrea Dawn. "Deposition, surface chemistry, and electrochemistry of YBa₂Cu₃O₇₋(subscript delta) materials." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3036611.
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Gerleman, Ian Gregory. "Thermo-electric properties of two-dimensional silicon based heterostructures." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343787.
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Ellerby, Donald Thomas. "Processing and mechanical properties of metal-ceramic composites with controlled microstructure formed by reactive metal penetration /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/10583.
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Guldeste, Ayhan. "Bismuth based thin film superconductors." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:681efdc0-8cba-4b3d-83eb-e0021eea5135.
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This thesis describes investigations performed into the growth and characterisation of Bi-based (Bi2Sr2Can-1CunO2n + 4 + x, n=2, 3) ceramic superconducting material in the form of thin films, about 0.5μm thick, grown on single crystal MgO, LaAIO3 and SrTiO3 substrates by r.f. magnetron sputtering. The effect of oxygen content on the Pb doped Bi-2223 (n=3) phase was also studied by changing the cooling process and by annealing in different partial pressures of oxygen at ambient pressure. The films produced have been assessed by considering their initial composition where it is found that Bi/Sr ratios can be between 0.9
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Ahmed, Savant. "Stereochemical structure-property relationships in polynorbornene from simulation." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/11805.
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Zhan, Xiaowen. "DEFECT CHEMISTRY AND TRANSPORT PROPERTIES OF SOLID STATE MATERIALS FOR ENERGY STORAGE APPLICATIONS." UKnowledge, 2018. https://uknowledge.uky.edu/cme_etds/88.
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Replacing organic liquid electrolytes with nonflammable solid electrolytes can improve safety, offer higher volumetric and gravimetric energy densities, and lower the cost of lithium-ion batteries. However, today’s all-solid-state batteries suffer from low Li-ion conductivity in the electrolyte, slow Li-ion transport across the electrolyte/electrode interface, and slow solid-state Li-ion diffusion within the electrode. Defect chemistry is critical to understanding ionic conductivity and predicting the charge transport through heterogeneous solid interfaces. The goal of this dissertation is to analyze and improve solid state materials for energy storage applications by understanding their defect structure and transport properties.
I have investigated defect chemistry of cubic Li7La3Zr2O12 (c-LLZO), one of the most promising candidate solid electrolytes for all-solid-state lithium batteries. By combining conductivity measurements with defect modeling, I constructed a defect diagram of c-LLZO featuring the intrinsic formation of lithium vacancy-hole pairs. The findings provided insights into tailoring single-phase mixed lithium-ion/electron conducting materials for emerging ionic devices, i.e., composite cathodes requiring both fast electronic and ionic paths in solid-state batteries. I suggested that oxygen vacancies could increase the Li-ion conductivity by reducing the amount of electron holes bound with lithium vacancies.
Using a simpler but also attractive solid electrolyte Li2ZrO3 (LZO) as an example, I significantly improved Li-ion conductivity by creating extra oxygen vacancies via cation doping. In particular, Fe-doped LZO shows the highest Li-ion conductivity reported for the family of LZO compounds, reaching 3.3 mS/cm at 300 °C. This study brought attentions to the long-neglected oxygen vacancy defects in lithium-ion conductors and revealed their critical role in promoting Li-ion transport. More importantly, it established a novel defect engineering strategy for designing Li-oxide based solid electrolytes for all-solid-state batteries.
I surface-modified LiNi0.6Co0.2Mn0.2O2 cathode material with a LZO coating prepared under dry air and oxygen, and systematically investigated the effect of coating atmosphere on their transport properties and electrochemical behaviors. The LZO coating prepared in oxygen is largely amorphous. It not only provided surface protection against the electrolyte corrosion but also enabled faster lithium-ion transport. Additionally, oxygen atmosphere facilitated Zr diffusion from the surface coating to the bulk of LiNi0.6Co0.2Mn0.2O2, which stabilized the crystal structure and enhanced lithium ion diffusion. Consequently, LiNi0.6Co0.2Mn0.2O2 cathodes coated with Li2ZrO3 in oxygen achieved a significant improvement in high-voltage cycling stability and high-rate performance.