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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Optimization studies on thermal and mechanical manufacturing processes for multifilament superconducting tape and wire

Basaran, Burak 15 November 2004 (has links)
There are many parameters that significantly affect the electrical performance of ceramic-core superconducting composite wire and tapes, which remain ambiguous and require more labor on their optimization. BSCCO 2212 has not been paid the attention and investment it deserves. In this regard, all optimization efforts were made for BSCCO 2223. In our work, a practical and inexpensive manufacturing method, thermally and mechanically optimized for Pb doped BiSrCaCuO 2212 superconducting multifilament (38 filaments) wires and tapes, was successfully employed. Optimized parameters can be classified under material, mechanical (deformation) and heat treatment (thermal) subgroups. Parameters involved with materials included investigation of deformation behavior of two different sheath metals; pure silver and 0.02% magnesia dispersion reinforced silver alloy. Pb doped BiSrCaCuO 2212 ceramic superconductor powder, the other source of material related parameters, was synthesized following the "Thermal Co-decomposition or Wet Mix" method. Fabrication of mono and multifilament wires with Oxide Powder in Tube (OPIT) method followed next. Optimization of drawing deformation was practiced to achieve the best ceramic grain alignment and smoother ceramic powder core/metal sheath interface in order to avoid "sausaging" in wires. Rolling of the wire products into tapes by following different deformation regimes was the other manufacturing stage of the project. Variable and constant reduction-per-pass deformation paths were employed to reveal their effects on our composites with distinct sheath material and filament formation. The search for the best (optimum) heat treatment schedule for our Bi2212 superconductor composites, a modified version of "step solidification partial melting", was employed successfully. A solution through tried recipes for the bubbling problem that occurred with our tapes was also addressed. Electrical performance tests of fully reacted wires were carried out in our laboratory and very promising results were attained.
2

Obtenção de filmes finos supercondutores do sistema BSCCO dopados com prata

Torsoni, Guilherme Botega [UNESP] 13 June 2008 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-13Bitstream added on 2014-06-13T20:33:17Z : No. of bitstreams: 1 torsoni_gb_me_ilha.pdf: 4414894 bytes, checksum: 9685dbff5ed635df09cc7fa100ae8308 (MD5) / Baterias Ajax / Filmes de BiPbSrCaCuO vem sendo estudados a muito tempo por muitos pesquisadores, onde já foram caracterizados de várias formas, tanto estrutural como eletricamente. O presente trabalho trata de modificações estruturais do composto por meio da dopagem; onde filmes de BPSCCO foram dopados com Ag para assim tentar melhorar as características do material, como a largura da transição na temperatura crítica (Tc) e a densidade de corrente crítica (Jc). Trabalhos anteriores feitos com bulks mostraram que com o mesmo tipo de dopagem, obtiveram-se maiores densidades de correntes para determinados valores de porcentagem de dopante, porém obtendo uma dependência não linear da densidade de corrente pela porcentagem de dopante. No presente trabalho foi utilizado um processo químico na obtenção de filmes, devido à facilidade em se efetuar a mistura e a homogeneização dos compostos precursores. Assim desenvolveu-se uma metodologia baseada na mesma empregada por M. Pechini, onde foram produzidas amostras dopadas com 0, 5, 10, 15 e 20% em peso de Prata, obtendo-se filmes da ordem de μm. Para as caracterizações elétricas dos filmes foi utilizada a técnica de quatro pontas dc, obtendo-se o comportamento da resistência em função da temperatura e também da Tensão pela corrente elétrica aplicada, para caracterização da Tc e Jc, respectivamente. Os resultados das caracterizações elétricas mostraram que para todas as amostras houve transições supercondutoras, a amostra dopada com 5% de Ag obteve-se o mais alto valor de Tc=93K. Para as medidas de Jc, os gráficos também mostraram um pico na amostra com 5%, e para as outras amostras não houve nenhuma mudança significativa, indicando que pode existir certa relação com os resultados encontrados na literatura. Pelos resultados obtidos, pode-se considerar que a metodologia aplicada pode se tornar extremamente promissora na obtenção... / Films of BiPbSrCaCuO have been studied by many researchers during a long time, which have been characterized by different ways such as structural and electrically. In this work it has submitted to some structural modifications of the compound through doping. Films of BPSCCO were doped with Ag for an attempt to improve their characteristics such as the width of the transition in critical temperature (Tc) and the critical current density ( Jc). Some previous works with bulks showed that, with the same type of doping, it has achieved higher values of current densities dependent of the percentage of doping, but obtaining a non-linear dependence of the current density with percentage of doping. In this work was a chemical process used to obtain superconductor films, because it is easy to do the mixture and the homogenization of precursor compounds, so it has developed a methodology based on the same employed by M. Pechini, where the films were doped with 0, 5, 10, 15 and 20% silver in weight, resulting in films with thickness around a few μm. In the electrical characterization of the films the four points DC technique was used, of resulting in the behavior of resistance depending on the temperature and voltage in function of the electrical applied current, to characterize the Tc and the Jc, respectively. The electrical characterization results showed that for all samples have superconducting transitions, but the sample doped with 5% of Ag presented the highest value of Tc = 93K. For Jc measurements, the graphs also showed a peak in the sample with 5% in agree with observed before, and for other samples were not observed significant change, indicating that there is some agreement with the results found in the literature. Based in the obtained results, may consider that the applied methodology can become extremely promising to obtain high quality films with the aim to conduce technological applications.
3

Angular Dependence of the Emission from the Intrinsic Josephson Junction in Pie-Shaped Wedge Triangular BSCCO Mesas

Morales, Manuel 01 May 2015 (has links)
The purpose of this thesis is to determine the radiation patterns from an acute isosceles triangular superconducting mesa modeled by a pie-shaped geometry. The terahertz band lies between the microwave and infrared regions of the electromagnetic spectrum. The terahertz radiation from atomic-scale layered superconducting mesas is caused by the tunneling of electron pairs in the ac-Josephson effect. To determine the terahertz power radiated per unit solid angle of an acute isosceles triangular superconducting mesa, a model was employed in which the shape of the mesa is approximated as a pie-shaped wedge. This model is shown to have an accuracy of about 1%. Using Love’s Equivalency Principle, the current caused by the Josephson effect is then assumed to be on the edges of the mesa. Since in the mesas used for experiments the electric field is in the direction of the current, it is parallel to the boundary of the sample. Hence, we want the TM modes, and that requires the magnetic field to be transverse to the boundary. We thus require that the tangential component of the magnetic field parallel at the boundary vanishes. Love’s equivalency principle provides the easiest and most straight forward way to satisfy this condition. The surface electric current density was modeled by comparing the magnetic vector potential resulting from the modeled edge current with that given by a standard volume average integration technique. The surface current density that provided the best approximation to the bulk average was used and the radiation patterns were plotted using Mathematica software.
4

Angle-Resolved Photoemission Studies on High Temperature Superconductor Bi2Sr2CuO6+[delta]

Pan, Zhihui January 2008 (has links)
Thesis advisor: Hong Ding / High temperature superconductivity has been one of the most challenging problems in condensed matter physics since its discovery. This dissertation presents systematic studies on electronic structures of single layer high temperature supconductor Bi2Sr2CuO6+[delta] by angle-resolved photoemission spectroscopy. A high binding energy band anomaly is observed in PbxBi2−xSr2CuO6+[delta]. Comparing with LDA calculation, the band is highly remonetized by a factor of 3, the incoherent part coexists and forms a band anomaly as a non-dispersive dive structure. Systematic studies are performed on Bi2+xSr2−xCuO6+[delta] with a wide doping range, revealing a linear doping nature of Bi substitution. An unusual Coulomb gap is observed in the heavily substituted samples. Our results reveal the dual role of off-plane chemical substitution in high-TC cuprates and elucidate the nature of the quantum electronic nature due to strong correlation and disorder. High resolution ARPES on LaxBi2Sr2−xCuO6+[delta] observes a large gap and a small gap coexisting at antinodal region below TC. The small gap is d-wave like and attributed to superconductivity, while the large gap is attributed to a CDW order. A strong short-ranged correlation between the small and large gap magnitude suggesting that superconductivity and charge ordering are driven by similar physical mechanism. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.
5

Terahertz Radiation from High-Temperature Superconducting BSCCO Mesas of Various Geometries

Cerkoney, Daniel P. 01 December 2015 (has links)
The purpose of this thesis is to examine the radiation from high-temperature superconducting mesas of Bi2Sr2CaCu2O8+ (BSCCO). This is motivated by the need for coherent sources of continuous wave terahertz (THz) emission capable of radiating practically in the THz frequency band. As BSCCO has been shown to be tunable from 0.5–2.4 THz (i.e., through the entire socalled terahertz gap centered about 1 THz), and has a higher peak operating temperature near 1 THz than most alternative sources, it is a good candidate for imaging and spectroscopy device applications [1]. When a static DC voltage is applied to a BSCCO mesa, the stack of Josephson junctions intrinsic to this type-II layered superconductor synchronously radiate. Adjustment of the bath temperature and applied voltage allows for the high degree of tunability observed for such an emitter [2]. To determine the angular dependence of radiation from BSCCO mesas, the dual source model from antenna theory is employed, and Love’s equivalence principle is used to simplify this framework. The total emission power obtained in this manner for the pie-shaped wedge is then fit to experimental results for a thin isosceles triangular mesa using the method of least squares, resulting in a standard deviation of = 0:4657. Additionally, symmetry is shown to play a significant role in the emissions for the transverse magnetic (TM) cavity modes of the equilateral triangular mesa. When the full group symmetry is imposed, the density of allowed modes is heavily diminished, and the original first excited even mode becomes the C3v symmetric ground state. These results for the equilateral triangle suggest, along with earlier experiments on the regular pentagonal mesa [3], that symmetry breaking effects can be used for purposes of tuning the characteristic frequency and angular dependence of the power radiated from BSCCO mesas with a high degree of symmetry.
6

Impressão direta na produção de filmes cerâmicos supercondutores e viabilidade do uso de camada tampão de CeO2 via rota química /

Souza, Gisele Aparecida de. January 2018 (has links)
Orientador: Rafael Zadorosny / Resumo: Neste trabalho é apresentada a produção de condutores revestidos de material supercondutor (superconducting coated conductors – SCC), ou seja, um filme supercondutor cerâmico, obtido por impressão direta da solução precursora sobre um substrato. Este processo foi estudado com o intuito de aplicar uma técnica de fabricação simples e de baixo custo visando a obtenção de filmes de boa qualidade a um custo reduzido. As soluções precursoras de CeO2, BSCCO e YBCO foram obtidas pelo método Pechini, considerada uma rota de produção de baixo custo. A fim de comparar a impressão direta com outra técnica, foram produzidos os mesmos filmes por spin coating. Para se obter os SCC, foi adicionada Ag às soluções dos materiais cerâmicos verificando sua incorporação na estrutura do filme e não apenas como um material de revestimento (como ocorre com as fitas supercondutoras de segunda geração). As caracterizações morfológicas e estruturais foram realizadas para identificar e analisar o processo de impressão direta do SCC. Já o comportamento supercondutor do material foi verificado através de medidas de R x T. / Abstract: This work presents the production of superconducting coated conductors (SCC), that is, a superconducting ceramic film obtained by direct printing of the precursor solution on a substrate. This process was studied with the intention of applying a simple and low cost technique focusing in the obtaining of good quality films at a reduced cost. The precursor solutions of CeO2, BSCCO and YBCO were obtained by the Pechini method, also considered a low cost production route. In order to compare direct printing with another technique, the same films were produced by spin coating. In order to obtain the SCC's, Ag was added to the solutions of the ceramic materials to incorporate in the film structure and not just as a coating material (as with second-generation superconducting tapes). Morphological and structural characterizations were performed to identify and analyze the SCC obtained by direct printing process. The superconductive behavior of the material was verified by measurements of R x T. / Doutor
7

Preparação e caracterização de filmes supercondutores do sistema BSCCO

Peruzzi, Raphael Otávio [UNESP] 15 September 2006 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-09-15Bitstream added on 2014-06-13T20:26:57Z : No. of bitstreams: 1 peruzzi_ro_me_ilha_prot.pdf: 4445456 bytes, checksum: 0e311bb9932e4122acd64b8b3ac049c8 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Devido a grande preocupação em se desenvolver novos materiais e técnicas para suprir a necessidade por novos recursos e atender com maior comodidade e eficiência a população mundial, estão surgindo novas áreas de pesquisas que visam suprir esta deficiência, seja criando novas tecnologias, ou mesmo aprimorando as técnicas existentes a fim de se obter um melhor aproveitamento dos recursos já existentes. Assim, estamos nos interessando por um ramo da ciência pouco conhecido, mas com um potencial muito elevado a ser descoberto, estamos falando dos materiais supercondutores, que pouco se sabe a respeito deles, porém muito já se faz com os mesmos. Desta maneira estamos apostando numa área mista, onde não usaremos os materiais supercondutores como sendo meramente condutores de energia e sim como dispositivos eletrônicos. Então, começamos o nosso trabalho, desenvolvendo materiais supercondutores na forma de filmes finos que é a base para o desenvolvimento desses dispositivos. Sendo assim escolhemos o sistema BSCCO, que tem como base os seguintes elementos, Bismuto, Estrôncio, Cálcio, Cobre e Oxigênio e que pode apresentar uma temperatura de transição da fase condutora para a fase supercondutora na faixa de 35 - 110K. Deste modo, nos propomos a estudar este tipo de material e desenvolver filmes finos, capazes de serem usados como... / Due to great concern in developing new materials and techniques to supply the need for new resources and to assist with larger comfort and efficiency the world population, new areas of researches that seek to supply this deficiency are appearing, by creating new technologies, or even improving the existent techniques in order to obtain a better use of the resources already existent. Like this, we are being interested in a branch of the little known science, but with a very high potential to be discovered, we are talking about the superconductor materials, that little it is known regarding them. However it is much already done with the same ones. In this way we are betting in a mixed area, where we won't use the superconducting materials as being merely drivers of energy but like electronic devices. Then, we began our work, developing superconductor materials in the form of thin films that is the base for the development of those devices. The system BSCCO was chose because it has composed by the following elements, Bismuth, Strontium, Calcium, Copper and Oxygen and that it may present a transition temperature of the conductive phase for the superconductive phase in the range of 35 - 110K. This way, we have studied this material type and to develop thin films, capable of be used as base for electronic devices. In our work we ...(Complete abstract click electronic access below)
8

Bi-Sr-Ca-Cu-O thin films grown by flash evaporation and pulsed laser deposition

Ganapathy Subramanian, Santhana 30 September 2004 (has links)
Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) compounds are an important family of compounds that have one of the highest transition temperatures among all high-temperature superconductors. The compound is known to exist in three distinct phases, commonly referred to as the 2201, 2212 and 2223 phases. Of these three phases, the 2212 and 2223 phases are the most important, as their transition temperature is higher than the boiling point of liquid nitrogen. It is desirable to produce the compound in thin film form, as the bulk samples are normally polycrystalline. This thesis compares thin films produced by two techniques for depositing BSCCO in order to understand the effect of various processing parameters on the final quality of the thin films. Thin films were grown by flash evaporation at Texas A&M University, and by pulsed laser deposition (PLD) at the University of Wollongong, Australia. The latter of these techniques is widely used for growing thin films of various compounds. Single-phase 2212 films were grown on a MgO substrate using the pulsed laser deposition technique from commercially available 2212 powder. The effect of annealing on the thin films was also studied.
9

Fabricação e caracterização de fios supercondutores do sistema BSCCO pelo método Powder-In-Tube (PIT)

Souza, Élton José de [UNESP] 25 March 2011 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-25Bitstream added on 2014-06-13T18:07:48Z : No. of bitstreams: 1 souza_ej_me_ilha.pdf: 1547635 bytes, checksum: a172b140a906aaf73e717b9702550ed0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Com o surgimento da supercondutividade as pesquisas envolvendo aplicações desta, em especial no transporte de energia, obtiveram um avanço promissor ao longo dos anos. Assim, este trabalho objetivou a fabricação de fios supercondutores utilizando o método Powder-In-Tube (PIT), no qual foi inserido dentro de um tubo de prata o pó da cerâmica supercondutora do sistema BSCCO. Estudos preliminares foram feitos em pastilhas feitas com o mesmo material supercondutor e após alguns resultados foram confeccionados os fios supercondutores. Medidas de caracterização foram feitas dentre elas a difratometria de raios-X, medidas elétricas pelo método de quatro pontas e microscopia do tipo (FEG-MEV) equipado com EDS para determinar a morfologia e composição química dos elementos na amostra. Os resultados de difratometria de raios-X apresentaram a formação das fases desejadas do sistema BSCCO de diferentes concentrações dentre elas as fases Bi-2212 Bi- 2223 e Bi-2234 contidas nas amostras sintetizadas. As medidas elétricas detectaram uma queda abrupta na resistência elétrica dos fios mostrando a faixa de transição supercondutora das amostras estudadas. As medidas de densidade de corrente com base no critério de corrente de 1μV/cm, utilizadas nos fios confeccionados, foram obtidos valores da ordem de 1,30 – 3,90 (KA/m2). Nas imagens de microscopia vale ressaltar uma melhora na interação entre os grãos supercondutores nas amostras submetidas a um maior tempo de sinterização e também foi possível verificar e analisar através da extrusão a compactação do pó cerâmico dentro do tubo de prata. O EDS detectou a composição química dos elementos nas amostras bem como a concentração das fases em determinadas regiões analisadas / With the emergence of superconductivity research involving applications of this, particularly in the transport of energy, had a promising advance over the years. This study aims to manufacture superconducting wires using the method Powder-In-Tube (PIT), which was inserted inside a tube of silver powder of superconducting ceramic BSCCO system. Preliminary studies were done on pellets made with the same superconducting material, and after some results were prepared the superconducting wires. Characterization measurements were made among them the X-ray diffraction, electrical measurements by the method of four points and type of microscopy (FEG-SEM) equipped with EDX to determine the morphology and chemical composition of the elements in the sample. The results of X-ray diffraction showed the formation of the desired phases for this type of superconductor, ie the BSCCO system between them was possible to determine the Bi-2212 phase, Bi-2223 and Bi-2234 contained in the synthesized samples. The electrical measurements have detected a sudden drop in electrical resistance of the wires showing the range of superconducting transition with good accuracy. It was possible to perform the calculation of current density in the wires made based on a criterion of 1 μV/cm were obtained and values of around 1,30– 3,90 (KA/m2). The values are consistent with the specifications of the samples and within the limits of our research. In microscopy images is noteworthy improvement in the interaction between the superconducting grains in samples submitted to a higher sintering time and it was possible to verify and analyze the compaction of ceramic powder into silver tube through the extrusion process. The EDX detected the chemical composition of the elements in the samples in a qualitative way
10

Power Distribution of Terahertz Emission from Hexagonal BSCCO Microstrip Antennas

Davis, Andrew E 01 January 2017 (has links)
We analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the high-Tc superconductor Bi2Sr2CaCu2O8+x (BSCCO). We discuss the C6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closed-form and non-closed-form solutions. The closed-form wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform part of the AC Josephson current and from the resonant cavity modes are derived. The wavefunctions and angular distribution of radiation from both sources are plotted for sixteen of the lowest-energy modes. Finally, we comment on the relevance of these power distributions to hexagonal arrays of equilateral triangular MSAs and propose a strategy for studying the non-closed-form modes.

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