Dissertations / Theses on the topic 'YBa2Cu3O7'

Orientadora: Profa. Dra. Marcia Tsuyama Escote<br>Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016.<br>Este trabalho descreve o processo de sintese dos compostos YBa2(Cu1-xNix)3O7-¿Â (x = 0; 0,01; 0,02 e 0,04) com diferentes microestruturas. As amostras foram preparadas na forma de fios micrometricos e pos a partir do metodo de precursores polimericos e pelo metodo de eletrofiacao, respectivamente. No caso das amostras eletrofiadas, varios fatores foram avaliados como o solvente, o polimero, a viscosidade, tensao aplicada entre a agulha e a distancia anteparo e agulha. As melhores condicoes utilizadas para produzir os fios de YBa2(Cu1-xNix)3O7-¿Â foi a que utilizou como solvente uma solucao contendo acido propionico-metanol-acido acetico e o polimero PVP, que auxilia no processo de eletrofiacao. Apos a etapa de sintese, as condicoes de tratamento termico foram estimadas a partir de medidas de analise termogravimetrica e analise termica diferencial. A partir destes resultados as amostras na forma de fios e pos foram tratadas termicamente entre temperaturas variando de 350 a 925 ¿C em atmosfera de oxigenio. As propriedades fisicas das amostras foram caracterizadas por meio de microscopia eletronica de varredura (MEV), de difracao de raios X (DRX), medidas de magnetizacao e transporte eletrico. O estudo de formacao da fase cristalina YBCO tambem foi analisado por meio de DRX, que verificou os resultados previos da analise termica e indicou que as melhores caracteristicas cristalograficas foram alcancadas quando as amostras foram tratadas termicamente a temperaturas > 900 ¿C/O2. Analise dos dados de DRX indicaram que todas as amostras cristalizam em uma estrutura ortorrombica (grupo espacial Pmmm), no entanto a maioria das amostras apresentaram picos pertencentes a fases adicionais identificadas como o BaCuO2 e CuO. Apesar disto, todas foram analisadas pelo metodo de Rietveld, os dados estruturais obtidos revelaram valores de parametros de rede proximos aqueles listados na literatura. Os parameros a, b e c das amostras de fios, apresentaram valores ligeiramente menores dos aqueles obtidos para os pos, tambem notou-se uma clara reducao do volume da cela unitaria, o que acredita-se estar relacionado ao metodo de sintese. Os parametros de rede c apresentam valores proximos daqueles esperados para a estequiometria YBa2Cu3O7. As amostras na forma de fios tambem apresentaram uma menor proporcao de fase adicional. As caracteristicas microestruturais verificadas por meio de imagens de MEV revelou que as amostras produzidas a partir de fios de YBa2(Cu1-xNix)3O7 perderam a forma de fio quando tratadas termicamente, apenas a amostra com x = 0 mantem a forma de fio. Estas apenas mantem a forma se tratadas termicamente a tempos e temperaturas menores, mas nestas condicoes perdem suas caracteristicas supercondutoras. Por isso, as amostras submetidas a tratamentos termicos em temperaturas 925¿C/O2 foram caracterizadas por meio de medidas de magnetizacao e transporte eletrico. As caracterizacoes magneticas revelaram que as amostras preparadas a partir dos pos e fios apresentaram a transicao supercondutora em Tc ~ 90-92 K, sendo que a substituicao de Cu por de Ni promoveu a diminuicao de Tc. E importante observar que nos pos esta variacao foi de 92 para 88 K para amostras com x variando de 0 a 0,04, enquanto que para as amostras eletrofiadas esta variacao foi de 92 para 90,2 K. Nas medidas de transporte eletrico verificou-se que a substituicao Cu por Ni nao promoveu variacoes significativas de Tc que foi da ordem de 86-88 K tanto para as amostras obtidas de pos quanto de fio. De forma geral, este trabalho produziu pos e fios de YBCO com qualidade similar a descrita na literatura, a eletrofiacao tambem permitiu a fabricacao de amostras de YBa2(Cu1-xNix)3O7 (x= 0,01; 0,02 e 0,04) com caracteristicas estruturais e supercondutoras ligeiramente diferentes daquelas obtidas por meio de sintese convencional de po.<br>This work describes the synthesis process of YBa2(Cu1-xNix)3O7-ä (x = 0, 0.01, 0.02 and 0.04) compounds with different microstructure. Micrometric wires and powder samples were prepared through electrospinning and polymeric precursor method, respectively. In the case of electrospinning samples several factors were evaluated like the solvent, polymer, viscosity, electrode-needle applied voltage and the work distance. The best conditions to obtain YBa2(Cu1-xNix)3O7-ä wires were the solution with propionic acid- methanol-acetic acid solvents, and with PVP polymer, which usually helps the electrospinning process. After the synthesis, the heat treatment conditions were estimated through thermogravimetric analysis and differential thermal analysis. With these results, two baths of wires and powders samples were heat-treated in temperatures varying from 350 to 925 °C in oxygen atmosphere. All samples physical properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), magnetic and electrical transport properties. The YBCO crystalline phase formation was also analyzed through XRD, it showed a similar results than those from thermal analysis. These results showed that better crystallographic characteristics were reached when the samples were heat treated in temperatures > 900 °C/O2. XRD analysis indicated that all samples crystallized in orthorhombic structure (Pmmm space group symmetry), though most of them presents peaks of addition phases identified as BaCuO2 and CuO. Even though all samples were analyzed through the Rietveld method, such structural data revealed lattice parameters values close to those reported in literature. It should be noticed that a, b and c values of the wire samples were slight smaller than those obtained to the powder samples, also there is a clear reduction of the unit cell volume, which we believe is related to the synthesis method. The c lattice parameters present values close to those expected to the YBa2Cu3O7 stoichiometry. The wire samples also present a small amount of additional phases. Microstructural characteristics were verified through SEM images, which revealed that the YBa2(Cu1-xNix)3O7 wire samples lost the wire shape after the heat treatment, only the YBCO samples maintain the wire shape. Samples only maintain this shape when they were heat treated at smaller times and lower temperature, but in this case they lost their superconductor characteristic. So, only samples obtained through heat treatments at 925°C/O2 were characterized by magnetization and electric transport. Magnetic measurements of samples prepared from powder and wires revealed a superconductor transition temperature in Tc ~90-92K, whereas the Cu for Ni substitution promoted a decrease of Tc. It is important to notice that Tc values vary from 92 to 88 K for the powers samples with x varying from 0 to 0.04, though for electrospinning samples this variation is from 92 to 90.2 K. In electrical transport measurements it was verified that such Cu to Ni substitution do not promote significant variations in the Tc, which was of the order of 86-88 K for both samples produced by powder and wires. As a general remark, this work produced powders and wires of YBCO with similar quality than those described in literature. Also, the electrospinning allowed the preparation of YBa2(Cu1-xNix)3O7 (x= 0.01; 0.02 e 0.04) samples with structural and superconductors characteristic slightly different from those obtained through powder conventional synthesis.

La superconductividad es el fenómeno que se da en algunos materiales metálicos y cerámicos. Se caracteriza por tener resistencia cero y ser diamagnéticos puros, presentándose a temperaturas menores a la temperatura critica. Existen dos tendencias principales para el estudio de los superconductores, teoría BCS y el método de ondas de espin. La razón del presente trabajo es analizar los cerámicos YBa2Cu3O7 (Y123) y YBa2Cu4O8 (Y124) en el estado fundamental (T igual a 0), paramagnético con el programa TB-LMTO-ASA y en forma complementaria, el programa “Augmented Spherical Wave” (ASW). Específicamente, se presentan cálculos de las bandas de energía, densidad de estados, densidad de carga total y parcial, la función de localización electrónica y la energía total. Adicionalmente se ha calculado la transferencia de carga entre los diferentes orbitales sobrelapados; calculo que no se ha encontrado en la literatura. Con el paquete ASW se calcula la COOP y COHP, que son la cantidad y energía de los estados híbridos bonding-antibonding. Con estos cálculos se intenta obtener información sobre el mecanismo de interacción y las condiciones que llevan a estos sistemas a un estado superconductor. La estructura de Y123 parte de un apilamiento de celdas perovskitas triple del tipo ABO3 con deficiencia de átomos de oxigeno, en donde se forma los planos CU2O en los limites de la celda central, siendo estos los responsables de las propiedades superconductoras, existiendo además cadenas de CuO. La estructura Y124 consiste en 2 celdas de Y123 aumentando su longitud en el eje c y en donde una de estas celdas es desplazado por ½ b del parámetro de red.<br>-- The superconductivity is the phenomenon that occurs in some metals and ceramic materials. It is characterized by zero resistance and pure diamagnetism, appearing at temperatures below the critical temperature. There are two major trends for the study of superconductors, BCS theory and the method of spin waves. The reason of this study is to analyze the ceramics YBa2Cu3O7 (Y123) and YBa2Cu4O8 (Y124) in the paramagnetic ground state (T igual a 0), with the computer program TB-LMTO-ASA and in a complementary manner, with the "Augmented Spherical Wave" (ASW) package. In detail, calculations of the electronic energy bands, full and partial density of states, electronic localization function and electronic total energy are presented. Additionally charge transfer between overlapping orbitals has been calculated, calculation that has not been found in the literature. With the package ASW the COOP and COHP was calculated, which are the amount of energy between the bonding and antibonding hybrids. With these calculations we are trying to obtain information on the mechanism of interaction and the conditions that lead in these systems to a superconducting state. The structure of Y123 parts from a stack of triple perovskite cells of the type ABO3 with a defficiency of oxygen atoms, which form the planes CuO2 in the limits of the central cell, and which are responsible for the superconducting properties. In addition there exist CuO chains. The structure of Y124 consists of two Y123 cells with increasing length in the c-axes, where one of these cells is moved by ½ of the parameter b.<br>Tesis

In this work, electrical transport properties and the maximum current carrying capability of YBa2Cu3O7-[delta] thin films and so called quasi-multilayers are investigated. These samples are prepared with pulsed laser deposition on single-crystalline substrates (SrTiO3) as well as on biaxially textured Ni tapes. The critical current density of coated conductors is limited by small-angle grain boundaries in low magnetic fields, but by the intra-grain pinning properties in higher magnetic fields. Accordingly, these investigations are divided into two parts: In the first part, the limitation of the critical current density by grain-boundaries and grain boundary networks is investigated with the main focus on the influence of geometrical factors such as the conductor width or the grain aspect ratio. In the second part, a possible enhancement of the critical current density due to different doping types (atomar doping using Zn and precipitate doping using BaMO3 where M is a transition metal) will be discussed. Here, not only the irreversibility field but also the pinning behaviour in very low magnetic fields is of interest to better understand the pinning mechanism of thin films<br>In der vorliegenden Arbeit werden elektrische Transporteigenschaften und die maximale Stromtragfähigkeit von YBa2Cu3O7-[delta]-Dünnschichten und -Schichtsystemen, die mit Hilfe der gepulsten Laserdeposition sowohl auf einkristallinem Substrat, SrTiO3, als auch auf biaxial texturierten Ni-Bändern deponiert wurden, untersucht. Da in kleinen Magnetfeldern Kleinwinkelkorngrenzen die kritische Stromdichte in Bandleitern begrenzen, in höheren jedoch die Pinningeigenschaften der Körner, gliedern sich diese Untersuchungen in zwei Teile: Im ersten wird die Limitierung der kritischen Stromdichte jc durch Korngrenzen und Korngrenzennetzwerke näher untersucht, wobei besonders Geometrieeinflüsse, wie die Leiterbahnbreite oder das Aspektverhältnis der Körner, interessieren. Im zweiten wird eine mögliche Erhöhung der kritischen Stromdichte durch verschiedene Dotierungen (atomare Dotierung: Zn, Ausscheidungsdotierung: BaMO3, M Metall) erörtert. Dabei ist nicht nur das Irreversibilitätsfeld interessant, sondern auch das Pinningverhalten in sehr kleinen Magnetfeldern, da so die Pinningmechanismen in Dünnschichten besser verstanden werden können

Made available in DSpace on 2017-07-21T19:26:09Z (GMT). No. of bitstreams: 1 Thiago Luis Schneider.pdf: 9685610 bytes, checksum: 1d228206aa0873ceb2084087b0fc033f (MD5) Previous issue date: 2014-03-28<br>Abstract Abstract<br>Resumo Resumo

Ce manuscrit est consacré à l'étude des propriétés cristallographiques et physiques particulières aux films supraconducteurs constitués du composé YBa2Cu3O7 (YBCO) et aux superréseaux supraconducteur/isolant (YBCO/LAO)n. Le premier travail de cette thèse était d'optimiser la fabrication des films YBCO. Cette étape s'est traduite par la mise au point de méthodes d'analyses structurales et surtout par le développement d'un nouveau modèle physique. Ce dernier a permis de mettre en évidence une hétérogénéité des propriétés supraconductrices au sein des couches d'YBCO et d'extraire des profils de températures critiques dans l'épaisseur des films. Néanmoins, même après optimisation des films par le biais des paramètres de dépôt, nous n'avons pu obtenir une homogénéité de la température critique dans toute l'épaisseur des films. En suspectant les contraintes d'interfaces d'agir sur les propriétés physiques et cristallographiques, nous avons développé, à partir d'une nouvelle méthode de simulations des pics de diffraction X, la détermination d'un profil type de déformation des mailles YBCO le long de l'axe de croissance des films. Enfin, en ce qui concerne les superréseaux, nous avons constaté l'impact des épaisseurs respectives des couches sur les propriétés physiques et structurales et avons mis en évidences l'existence de défauts de différentes natures grâce à la microscopie électronique en transmission. Enfin l'application du modèle physique développé dans cette thèse nous a conduit à constater que seule une fraction d'une structure supraconductrice possédait effectivement cette propriété. Le point limitant ayant été identifié, il faut reconsidérer le processus de dépôt des films afin de s'affranchir de ce problème d'inhomogénéité au sein des films pour envisager la conception de systèmes électroniques complexes.

Ce manuscrit est consacré à l’étude des propriétés cristallographiques et physiques particulières aux films supraconducteurs constitués du composé YBa2Cu3O7 (YBCO) et aux superréseaux supraconducteur/isolant (YBCO/LAO)n. Le premier travail de cette thèse était d’optimiser la fabrication des films YBCO. Cette étape s’est traduite par la mise au point de méthodes d’analyses structurales et surtout par le développement d’un nouveau modèle physique. Ce dernier a permis de mettre en évidence une hétérogénéité des propriétés supraconductrices au sein des couches d’YBCO et d’extraire des profils de températures critiques dans l’épaisseur des films. Néanmoins, même après optimisation des films par le biais des paramètres de dépôt, nous n’avons pu obtenir une homogénéité de la température critique dans toute l’épaisseur des films. En suspectant les contraintes d’interfaces d’agir sur les propriétés physiques et cristallographiques, nous avons développé, à partir d’une nouvelle méthode de simulations des pics de diffraction X, la détermination d’un profil type de déformation des mailles YBCO le long de l’axe de croissance des films. Enfin, en ce qui concerne les superréseaux, nous avons constaté l’impact des épaisseurs respectives des couches sur les propriétés physiques et structurales et avons mis en évidences l’existence de défauts de différentes natures grâce à la microscopie électronique à transmission. Enfin l’application du modèle physique développé dans cette thèse nous a conduit à constater que seule une fraction d’une structure supraconductrice possédait effectivement cette propriété. Le point limitant ayant été identifié, il faut reconsidérer le processus de dépôt des films afin de s’affranchir de ce problème d’inhomogénéité au sein des films pour envisager application dans la conception de systèmes électroniques complexes<br>This manuscript is devoted to the study of crystallographic and physical properties of superconductor YBCO thin films and superconductor/insulator (YBCO/LAO)n superlattices. The first stage of this work was to optimize the YBCO thin film deposition. Elaboration of a new physical model allows us to determine a critical temperature distribution inside the films thickness. Nevertheless, no homogeneous critical temperature inside the films can be obtained. This work shows that the interface strains modify the crystallographic and physical properties. We developed a new simulation method concerning the XRD peak shape analysis which allows us to determine YBCO cell deformation profile along the axis. About superlattices, effects of thickness on the physical and structural properties have been noticed. Transmission Electron Microscopy exhibits existence of structural defects in the films. Ending, the physical model proposed in the present work provides important informations regarding the magnetic interaction between two superconductor layers, which seems to limit application of these superlattices in the realization of complex electronic devices

La microscopie electronique en transmission (met) avec ses derniers developpements en imagerie haute resolution (mehr) et en spectroscopie de pertes d'energie d'electrons (eels) a ete exploitee et developpee pour l'etude de l'ordre structural, de la composition chimique et de l'etat electronique jusqu'a l'echelle atomique de composes y#1ba#2cu#3o#7#-#. Dans le cas de films minces elabores par depot chimique en phase vapeur a partir de composes organometalliques sur differents substrats et pour plusieurs conditions d'elaboration, l'etude de la topologie en met puis de l'arrangement atomique local en mehr a permis de visualiser directement l'ensemble des imperfections structurales et/ou chimiques au sein du film et a l'interface avec le substrat jusqu'a l'echelle de la longueur de coherence. Des correlations avec les grandeurs physiques importantes pour les applications a l'electronique supraconductrice ont ete proposees. En eels, nous avons developpe l'etude parallele et complementaire des signatures associees a l'excitation des electrons faiblement lies et des electrons des niveaux atomiques profonds. Nous avons mis au point un logiciel d'analyse a partir d'un traitement de kramers-kronig du signal afin d'acceder a des informations sur la densite d'etats joints entre les bandes de valence et de conduction. Avec une resolution d'analyse d'un electron-volt, nous avons analyse les structures fines pres des seuils d'excitation o-k et cu-l#2#,#3 et correle les resultats aux etats inoccupes du diagramme de structure de bande. Nous avons aussi exploite les signatures des processus d'interaction electronique en fonction de la quantite de mouvement transferee controlee dans l'experience eels. L'application a y#1ba#2cu#3o#7#-# a permis d'evaluer , notamment a partir de la signature du plasmon de volume, ainsi que de reveler l'anisotropie des distributions electroniques entre le plan (a,b) et la direction c de la structure orthorhombique de y#1ba#2cu#3o#7#-#, a partir de l'etude du seuil o-k.

Grain boundaries form the basis of an important Josephson junction technology in the cuprates and also limit the superconducting critical currents attainable in practical, polycrystalline materials. An improved understanding of these defects is therefore important for applications. The status of the current understanding of cuprate grain boundaries is summarised and experimental investigations are presented, focusing on the less well understood high angle boundaries. Measurements of the capacitance of grain boundaries in the overdoped superconductor Y1-xCaxBa2Cu3O7-8, were performed as a function of the calcium content, using the Josephson coupling across the boundaries. Particular care was taken to eliminate the effects of heating and stray capacitance due to the substrate. The effect of thermal noise was also assessed. These measurements provide important information about the area and the width of the grain boundaries, that highlights their inhomogeneous nature. A new technique was applied to measure the normal state properties of YBa2Cu3O7-8 grain boundaries above the critical temperature. Since the resistance of the adjacent material at high temperatures is comparable to, or greater than, that of the grain boundary a compensating Wheatstonebridge structure was used. The errors involved in this technique are carefully assessed and quantified. The normal state resistance of a number of different grain boundary orientations was measured from room temperature to the critical temperature. Detailed characterisation of the grain boundaries, including measurements of the critical current and the current voltage characteristics at low temperatures, was performed. The results obtained are used to assess the validity of the various theories for the grain boundary electrical structure. A tunneling model that accounts for the band structure of the material is developed and applied to potential barriers consistent with a band bending model. This theory is shown to provide a convincing account of the experimental results presented in this thesis.

Large electrical current transport in the absence of energy losses is thekey factor in commercial applications of high temperature superconductors. This thesis demonstrates an easy and inexpensive bottom-uptechnique to produce self assembled nanorods, segmented nanorodsas well as nanoparticles in YBa2Cu3O7-δ thin films grown by pulsedlaser deposition. The structural and morphological characteristic ofthe pinning landscapes produced are investigated and correlated totheir effects on the superconducting properties of the thin films. In particular two pinning landscapes are investigated: Ba2YNbO6nanorods are grown in YBa2Cu3O7-δ thin films using a Ba2YNbO6doped YBa2Cu3O7-δ pulsed laser deposition targets andBa2(Y/Gd)(Nb/Ta)O6 segmented nanorods together with (Y/Gd)2O3nanoparticles are grown in (Y/Gd)Ba2Cu3O7-δ thin films using aBa2YNbO6 + Gd3TaO7 doped YBa2Cu3O7-δ pulsed laser depositiontargets. The Ba2YNbO6 + YBa2Cu3O7-δ is deeply characterised and the effectsof the deposition parameters are analysed. Ba2YNbO6 is demonstratedto be an interesting novel pinning addition capable to increasethe critical current and to reduce the YBa2Cu3O7-δ critical currentsangular dependencies anisotropy. The Ba2YNbO6 + Gd3TaO7 + YBa2Cu3O7-δ is found to produce anew complex pinning landscape extremely effective. At high fieldsthe synergetic combination of the different defects typology is shownto generate an interesting new feature in the critical current angulardependencies. Chapter 1 is an introduction to superconductivity, the fundamentals ofthe field are briefly presented. In chapter 2 the discussion in focused onpinning in high temperature superconductors. Cuprates and in particularYBa2Cu3O7-δ are presented. The pinning phenomenon andthe practical pinning engineering in thin films is also discussed in thischapter. Chapter 3 describes the thin films preparation methods andthe characterisation techniques used in the research work. Chapter 4and 5 are focused on the Ba2YNbO6 doped YBa2Cu3O7-δ thin films. Chapter 4 is an introduction to Ba2YNbO6 doped YBa2Cu3O7-δ, thepreliminary results obtained on Ba2YNbO6 doped YBa2Cu3O7-δ thin films are shown in this chapter. The crystalline structure, the morphologyand the superconducting properties of thin films depositedadopting different deposition parameters are analysed and discussedin chapter 5. In chapter 6 the new complex pinning landscape ofBa2(Y/Gd)(Nb/Ta)O6 and (Y/Gd)2O3 in (Y/Gd)Ba2Cu3O7-δ is presented. Concluding remarks on the research described in the workends the thesis in a brief final chapter 7.

Dès la découverte des supraconducteurs à haute température critique, les recherches se sont intensifiées afin de comprendre les mécanismes qui sont à l'origine des propriétés de ces matériaux. L'état mixte, tout comme l'état supraconducteur pur et l'état normal, a fait l'objet de nombreux travaux de recherche. En particulier, la structure des vortex à l'état mixte, et leur mouvement sous l'effet d'une force quelconque, étaient et restent le centre de préoccupation. Les effets thermoélectrique (Seebeck) et thermomagnétique (Nernst) sont parmi les différentes mesures qui peuvent donner de l'information sur les états des vortex à l'état mixte. L'avantage essentiel de ces deux effets est l'absence d'un courant électrique appliqué. Ce dernier peut donner des perturbations indésirables durant les mesures. D'autre part, nous avons utilisé la méthode CA (Courant Alternatif) pour effectuer nos mesures. Cette méthode est caractérisée par une meilleure résolution par rapport à la méthode CC (Courant Continu) conventionnelle. Nous avons étudié autant des échantillons maclés que des échantillons sans macles. D'abord nous avons testé notre montage à champ magnétique nul. Nous avons alors montré que le pic rapporté par certains dans l'effet Seebeck à la transition supraconductrice ne correspond pas à une réalité physique mais à un artefact expérimental. On avait associé ce pic aux fluctuations. Par la suite, nous avons mis en évidence et étudié pour la première fois avec les effets Seebeck et Nernst le phénomène de la fusion du réseau de vortex grâce à des mesures sur les échantillons sans macles. Cette étude s'est faite pour deux concentrations d'oxygène différentes et pour un gradient de température parallèle, consécutivement, aux deux axes cristallographiques dans le plan ab. Finalement, nous avons étudié l'effet des plans de maclage sur le mouvement des vortex. Ceci a été réalisé en appliquant le gradient de température selon trois directions différentes (0, 45 et 90[degré]) avec les plans de maclage. Nous avons observé, pour le premier angle un mouvement libre du vortex, pour le second angle une contribution de l'effet Nernst à l'effet Seebeck et pour la troisième direction un phénomène d'activation. Dans ce dernier cas, les plans de maclage font un obstacle qui s'oppose au mouvement des vortex. De ce qui précède, nous concluons qu'avec la bonne résolution de notre technique nous sommes capables d'observer des phénomènes que la technique CC ne met pas en relief. D'autre part, la variété d'échantillons que nous avons étudiés et les phénomènes que nous avons observés valorisent la présente étude.

Made available in DSpace on 2017-07-21T19:25:56Z (GMT). No. of bitstreams: 1 pauladeazambuja.pdf: 3846623 bytes, checksum: 775b83dd168b0a44745812c2ca7a454a (MD5) Previous issue date: 2008-03-28<br>Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná<br>In this work is presented an experimental study on the effects of the addition of Ag to the system YBa2Cu3O7-d. The silver can be added to the YBa2Cu3O7-d system through the mixture with metallic Ag, with oxide of silver (Ag2O) or with nitrate of silver (AgNO3), using different techniques and forms of processing. The addition of silver to the YBa2Cu3O7-d system is known by minimizing the properties undesirable of the system, without deleterious effects in superconducting properties. She is responsible for the significant increase in the conductivity thermal and electric of the system; it improves of the mechanical properties, as the resistance of fracture and elasticity of the material, from the reduction of the porosity; it reduces the weak links between the superconducting grains, improving the contact between the same. The samples used in this work had been processed for different experimental routes: in the first set of samples Ag2O was added to the YBa2Cu3O7-d system previously prepared; on the second set of samples the silver oxide was mixed to the precursors Y2O3, BaCO3 and CuO and then the YBa2Cu3O7-d system was processed; and in the third set of samples metallic silver was added to the YBa2Cu3O7-d system previously prepared. The characterization of the samples, pure and doped with silver, was realized through with aid of different techniques enclosing: analysis of the crystalline structure; analysis of the superficial topology; measures calorimetric; mechanical properties; properties of electronic transport and magnetic properties. The obtained results are coherent with results of other works on composites YBa2Cu3O7-d/Ag and demonstrate that the addition of the silver to the YBa2Cu3O7-d system, of a general form, improves the properties of this system. Key Words: Superconductivity; YBa2Cu3O7-d system; processing of composites YBa2Cu3O7-d/ Ag; characterization of materials.<br>Neste trabalho é apresentado um estudo experimental sobre os efeitos da adição de Ag ao sistema YBa2Cu3O7-d. A prata pode ser adicionada ao sistema YBa2Cu3O7-d através da mistura com Ag metálica, com óxido de prata (Ag2O) ou com nitrato de prata (AgNO3), utilizando diferentes técnicas e formas de processamento. A adição de prata ao sistema YBa2Cu3O7-d é conhecida por minimizar as propriedades indesejáveis do sistema, sem deteriorar as propriedades supercondutoras. Ela é responsável pelo aumento significativo nas condutividades térmica e elétrica do sistema; melhora das propriedades mecânicas, como a resistência à fratura e elasticidade do material, a partir da redução da porosidade; reduz as ligações fracas entre os grãos supercondutores, melhorando o contato entre os mesmos. As amostras utilizadas neste trabalho foram processadas por rotas experimentais diferentes: no primeiro lote de amostras foi adicionado Ag2O ao sistema YBa2Cu3O7-d previamente preparado; no segundo lote de amostras o óxido de prata foi misturado aos precursores Y2O3, BaCO3 e CuO e então o sistema YBa2Cu3O7-d foi processado; e no terceiro lote de amostras prata metálica foi adicionada ao sistema YBa2Cu3O7-d previamente preparado. A caracterização das amostras, pura e dopada com prata, foi realizada com auxílio de diferentes técnicas abrangendo: análise da estrutura cristalina; análise da topologia superficial; medidas de calorimetria; propriedades mecânicas; propriedades de transporte eletrônico e propriedades magnéticas. Os resultados obtidos são coerentes com resultados de outros trabalhos sobre compósitos YBa2Cu3O7-d/Ag e demonstram que a adição da prata ao sistema YBa2Cu3O7-d , de uma forma geral, melhora as propriedades deste sistema.

1ere partie: nous presentons des resultats de diffusion raman sur des monocristaux de ybacuo a des temperatures au-dessus et en dessous de tc. L'analyse complete dans les differentes polarisations nous permet d'obtenir l'anisotropie des sections efficaces de diffusion de tous les modes ag, suivant les trois axes cristallographiques. La diffusion raman electronique presente aussi une reponse anisotrope. Nous montrons qu'il est possible de mesurer le gap supraconducteur. Nous obtenons une valeur du gap entre 3. 3 et 3. 5 ktc. Nous montrons que le comportement anormal en temperature du mode mou est compatible avec cette valeur. 2eme partie: nous presentons un dispositif de mesure inductive de la temperature critique d'un supraconducteur sous tres haute pression dans une cellule a enclumes diamant. Ce montage a ete utilise avec succes pour des monocristaux de yba2cu307 et yba2cu408 jusqu'a 15 gpa. Pour yba2cu307 tc decroit lineairement avec p avec une pente de 2. 5 k/gpa, a partir de 2 gpa. Pour yba2cu408 tc croit avec une pente de 5. 5 k/gpa a l'origine, l'effet commencant a saturer a partir de 3 gpa. Tc atteint une valeur de 106 k a 10 gpa. Le comportement oppose sous pression de ces deux composes est discute dans le cadre de modeles existant

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung neuer Schichtsysteme für die Realisierung biaxial texturierter hochtemperatursupraleitender Bandleiter. Bisher sind eine Vielzahl von Bandleiterarchitekturen bekannt, die sowohl durch physikalische Depositionsmethoden als auch mittels Abscheidung aus der chemischen Lösung hergestellt werden können. Während die Funktion von YBCO-Bandleitern mit Hilfe physikalischer Depositionsmethoden in den letzten Jahren demonstriert werden konnte, zeigen auf chemischem Wege deponierte Bandleiter schlechtere Eigenschaften. Seitens der Industrie besteht ein starkes Interesse, die hohen Produktionskosten, die im Hinblick auf physikalische Depositionsmethoden mit einem hohen Anlagenaufwand verbunden sind, anhand der kostengünstigen chemischen Synthese von Einzelschichten oder der gesamten Bandleiterarchitektur zu senken. Gelöst wurde diese Aufgabe innerhalb der vorliegenden Arbeit durch die Entwicklung metallorganischer Vorstufenlösungen zur Deposition von CaTiO3-, SrTiO3-Pufferschichten und supraleitender YBa2Cu3O7-Schichten.

The discovery of superconductivity in ceramic materials by Bednorz and Müller [2, 3] in early 1987, immediately followed by Wu et al. [4, 5] who showed that YBa2Cu3O7−x (YBCO) becomes superconducting (92K) well above the boiling point of nitrogen (77K) created a great excitement in superconductivity research. Potential applications of high Tc-superconductors require large critical currents and high-applied magnetic fields. Effective ways to increase the critical current density at high magnetic fields in YBCO are the introduction of nanoparticles and chemical substitution of yttrium by other rare earth elements. Since low costs and environmental compatibility are essential conditions for the preparation of long length YBCO films, the cost effective chemical solution deposition (CSD) procedure was selected, given that no vacuum technology is required. To reveal the flexibility and the good optimization possibilities of the CSD approach two main processes were chosen for comparison: a fluorine-free method, namely the polymer-metal precursor technique, and a fluorine-based method, the metalorganic deposition (MOD) using the trifluoroacetates (TFA) technique. Sharp transition temperature widths DTc of 1.1K for the polymer metal method, 0.8K for TFA method and critical current densities Jc of _3.5MA/cm2 shows that high quality YBCO thin films can be produced using both techniques. Especially interesting is the magnetic field dependence of the critical current density Jc(B) of the Y(Dy)BCO (80 %) films showing that for the lower magnetic fields the critical current density Jc(B) is higher for a standard YBCO film, but at fields higher than 4.5T the critical current density Jc(B) of Y(Dy)BCO is larger than that for the YBCO. Above 8T, Jc(B) of the Y(Dy)BCO film is more than one order of magnitude higher than in pure YBCO film<br>Die Entdeckung der Supraleitung in keramischen Materialien durch Bednorz und Müller 1987 und die kurz darauf folgende Beobachtung von Wu et al., dass YBa2Cu3O7−x (YBCO) supraleitende Eigenschaften deutlich oberhalb (92K) des Siedepunktes von Stickstoff (77K) aufweist, führten zu einer enormen Intensivierung der Forschung hinsichtlich neuer supraleitender Materialien sowie deren Eigenschaften und möglichen Einsatzgebieten. Potentielle Anwendungsgebiete für diese neuen Hochtemperatur-Supraleiter erfordern hohe kritische Stromdichten und hohe kritische Feldstärken. Effektive Wege zur Erhöhung der kritischen Stromdichte in starken Magnetfeldern in YBCO sind der Einbau von Nanoteilchen oder die chemische Substitution von Yttrium durch ein anderes Seltenerd-Element. Da niedrige Kosten und gute Umweltverträglichkeit wichtige Voraussetzungen für die Herstellung von YBCO-Schichten großer Länge darstellen, werden in dieser Arbeit die Vorteile und Einsatzmöglichkeiten der Chemischen Lösungsabscheidung (chemical solution deposition - CSD) untersucht. CSD Prozesse sind besonders gut geeignet, weil sie keine Vakuum-Technologie erfordern und einen hohen Grad an Flexibilität garantieren. Zur Demonstration der guten Optimierbarkeit werden zwei wichtige CSD-Verfahren miteinander verglichen: die Polymer-Metall Precursor Technik - eine Fluor-freie Methode - und die metallorganische Abscheidung mittels Trifluoroacetat (TFA-MOD), bei der Fluor zum Einsatz kommt. Scharfe supraleitende Übergänge (Polymer-Metall Precursor Technik: DTc = 1.1K; TFA -MOD: DTc = 0.8K) sowie hohe kritische Stromdichten von ca. 3.5MA/cm2 (B= 0 T) zeigen, dass mit beiden Verfahren dünne YBCO-Schichten hoher Qualität hergestellt werden können. Außerdem bieten CSD-Verfahren durch die hervorragende Kontrollierbarkeit der Stöchiometrie des Precursors die Möglichkeit Yttrium teilweise oder vollständig durch andere Seltenerd-Metalle zu ersetzen und damit die kritische Stromdichte in hohen Magnetfeldern deutlich zu erhöhen. In dieser Arbeit wird gezeigt, dass besonders die TFA-Methode besonders geeignet ist, um (RE)BCO-Schichten (RE: rare earth) herzustellen. Untersucht wurden verschiedene Zusammensetzungen mit Sm, Dy und Ho. Außerordentlich interessant sind dabei die Ergebnisse für Y(Dy)BCO-Schichten. Schichten mit einem Dy-Gehalt von 80 % zeigen oberhalb von 4.5T deutlich höhere kritische Stromdichten als reine YBCO Schichten. Bei Magnetfeldern größer als 8T beträgt der Unterschied mehr als eine Größenordnung

Superconducting materials exhibit effects which can be used to improve a wide range of existing technologies, and enable the creation of entirely new ones. The infinite conductivity of superconductors results in high specific power and efficiency, making them an attractive replacement for conventional conductors. By far the most technologically useful material is Yttrium Barium Copper Oxide (YBCO), which superconducts well above the temperature of cheap, readily available liquid nitrogen (77K), which makes cooling it to the required temperature economically viable. Improvement of flux pinning and thus the critical current, <i>J_c</i>, that can be carried in YBCO is crucial for achieving widespread applications of this technologically important material. This thesis presents an investigation into pinning in thin films of YBCO, via inclusions of a non-superconducting stable oxide phase, RE₃TaO₇, where RE = Sm, Gd, Er or Yb. This second phase provides both ideally sized <i>c</i> axis correlated and random pinning sites and results in an order of magnitude improvement of critical current over pure YBCO at 1 Telsa. Additionally, RE₃TaO₇ does not depress the superconducting transition temperature, as has been found with the closest performing additives based on BaWO₃, where W = Zr or Sn. The thin films studied were grown by pulsed laser deposition and characterised with a standard four point measurement technique, transmission electron microscopy, X-ray diffraction, atomic force microscopy and X-ray Photoelectron Spectroscopy. Additionally, the importance of surface pinning in doped films was investigated and the mixing of the second phase with YBCO during the initial layers of film growth was found to have a large effect of the pinning at that interface.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung neuer Schichtsysteme für die Realisierung biaxial texturierter hochtemperatursupraleitender Bandleiter. Bisher sind eine Vielzahl von Bandleiterarchitekturen bekannt, die sowohl durch physikalische Depositionsmethoden als auch mittels Abscheidung aus der chemischen Lösung hergestellt werden können. Während die Funktion von YBCO-Bandleitern mit Hilfe physikalischer Depositionsmethoden in den letzten Jahren demonstriert werden konnte, zeigen auf chemischem Wege deponierte Bandleiter schlechtere Eigenschaften. Seitens der Industrie besteht ein starkes Interesse, die hohen Produktionskosten, die im Hinblick auf physikalische Depositionsmethoden mit einem hohen Anlagenaufwand verbunden sind, anhand der kostengünstigen chemischen Synthese von Einzelschichten oder der gesamten Bandleiterarchitektur zu senken. Gelöst wurde diese Aufgabe innerhalb der vorliegenden Arbeit durch die Entwicklung metallorganischer Vorstufenlösungen zur Deposition von CaTiO3-, SrTiO3-Pufferschichten und supraleitender YBa2Cu3O7-Schichten.

Après la découverte de Bednorz et Muller de la supraconductivité à haute température critique dans des oxydes à base de cuivre, chu et wu annoncent une transition supraconductrice à 92 k pour le composé YBa2Cu3O7-x (0<x<1). Ce composé subit une transformation de phase quand le taux de lacunes augmente. La non-stoechiométrie en oxygène et la transition de phase orthorhombique-quadratique ont été étudiées de deux façons. En modélisant le composé par le plan de base cuo, le comportement thermodynamique du matériau est simulé par la méthode de Monte Carlo dans l'ensemble grand canonique. Les configurations du plan de base ainsi reproduites sont comparables à celles observées sur le composé réel et du point de vue thermodynamique, les courbes de variation de la dérivée de l'énergie par rapport à la température ont une forme caractéristique en et la courbe de dégénérescence de l'énergie ne présente qu'un seul pic. Ces deux résultats sont compatibles avec une transition du second ordre. La non-stoechiométrie à la transition est de 0,330,03. Pour l'étude expérimentale, nous avons conçu et réalisé deux appareillages : un fluxmètre thermique et une thermobalance. Les résultats de non-stoechiométrie sont interprétés par un modèle faisant intervenir des associations neutres de défauts ponctuels. Les effets thermiques associés à la transition ne se manifestent que par un décalage de la ligne de base en plein accord avec une transition du second ordre. La cinétique d'oxydation dix fois plus rapide que celle de la réduction met en jeu un mécanisme complexe impliquant la diffusion inter et intra granulaire.

YBa2Cu3O7-d (YBCO) was one of the first high temperature superconductors discovered, and its superconducting properties are strongly dependent on oxygen stoichiometry. A large amount of work has been done on the variation of stoichiometry and its effect on the superconducting properties of the material. However, in spite of all the work done, the results published in the literature are very scattered. This thesis presents a thermogravimetric study of oxygen diffusion in YBCO under isothermal and non-isothermal conditions and tries to reconcile the data available based on the results obtained and taking into account the factors that may have affected the data presented by other groups, such as the effects of the microstructure and the different diffusion coefficients measured with the techniques used. An Arrhenius expression for the chemical diffusion of oxygen has been calculated from the analysis of isothermal oxygenation data, and it has been corroborated by a study of the nonisothermal experiments carried out. This work includes the development of a macroscopic model for oxygen diffusion in YBCO based on the diffusion coefficient calculated from experimental data. The model is used to simulate for the first time oxygenations under both isothermal and non-isothermal conditions. The study of non-isothermal oxygenations has led directly to the design of novel cooling procedures that can be introduced at the end of the processing stage of YBCO samples, producing highly oxygenated specimens in shorter times than for conventional isothermal and ramped oxygenation procedures. The final section of this dissertation presents a study of the Direct Current Zoning effect. The generation of a mobile hot zone in a polycrystalline YBCO bar when passing a current across it is directly linked to the diffusion of oxygen ions in the material. A mechanism for the motion of the zone along the sample has been suggested. A computer model has been developed to reproduce this process taking into account the motion of ions due to chemical diffusion and the potential difference established. The results from this model have corroborated the mechanism suggested and give for the first time the opportunity to study this phenomenon in more detail.

This thesis deals with the transport properties and critical current limitations found in YBa2Cu3O7[-delta] coated conductors prepared by the &amp;quot;rolling assisted biaxially textured substrate&amp;quot; (RABiTS) approach. For this purpose a buffer layer system composed of CeO2 and yttria-stabilised zirconia, and subsequently a YBa2Cu3O7[-delta] film were epitaxially grown by pulsed laser deposition on a biaxially textured metallic substrate. The resulting texture of the YBa2Cu3O7[-delta] film is crucial for the achievement of high critical current densities. A propagation of the granular structure of the metallic substrate into the YBa2Cu3O7[-delta] film was detected, which leads to the formation of a YBa2Cu3O7[-delta] grain boundary network and limits the critical current density of the samples. In order to study this limitation, critical current measurements were performed on the prepared samples at different temperatures and magnetic fields, detecting a transition between intergrain and intragrain current limitation that occurs at the so-called crossover magnetic field. The crossover magnetic field was found to shift to lower values as the temperature was increased. It was concluded that the grain boundary network limits the critical current density of the YBa2Cu3O7[-delta] coated conductor only for magnetic fields below the crossover field<br>In der vorliegenden Dissertation werden Transporteigenschaften und die Limitierung der kritischen Stromdichte von YBa2Cu3O7[-delta] Bandleitern untersucht. Für die Präparation wird das epitaktische Schichtwachstum auf biaxial texturierten Substraten genutzt (RABiTS-Technik). Dabei wird mittels gepulster Laserdeposition eine Pufferschicht aus CeO2 und Yttrium-stabilisiertem Zirkonoxyd (YSZ) und anschließend eine YBa2Cu3O7[-delta] Schicht epitaktisch auf ein Substrat aufgebracht. Die resultierende biaxiale Textur der YBa2Cu3O7[-delta]-Schicht spielt eine Hauptrolle, um möglichst hohe Stromdichten zu erreichen. Es zeigte sich, daß die granulare Struktur des Substrates in die YBa2Cu3O7[-delta]-Schicht übertragen wird und zur Ausbildung eines Korngrenzennetzwerkes führt, welches wiederum die zu erwartende kritische Stromdichte begrenzt. Um die Wirkung des Korngrenzennetzwerkes zu untersuchen, wurden kritische Ströme der gewachsenen Schichten in Abhängigkeit der Temperatur und des angelegten Magnetfeldes gemessen. Es stellte sich heraus, daß die Limitierung des Stroms bei schwachen Magnetfeldern zwischen den einzelnen Körnern bestimmend ist, die dann bei größeren Feldern einer Strombegrenzung innerhalb der Körner weicht. Das beide Bereiche trennende Magnetfeld wird als Übergangsfeld bezeichnet. Daraus kann geschlußfolgert werden, daß das Korngrenzennetzwerk von YBa2Cu3O7[-delta] Bandleitern den Strom nur für magnetische Felder unterhalb des Übergangsfeldes begrenzt

Previous measurements show that the thermal conductivity of $Y Ba sb2 Cu sb3 O sb{7- delta}$ in the basal plane is anisotropic with a large peak in the superconducting state. The magnitude of this anisotropy in the superconducting and normal states, and the dominant mechanism for heat conduction in the superconducting state are currently the subject of debate. We have measured the thermal conductivity of high quality $Y Ba sb2 Cu sb3 O sb{7- delta}$ for deoxygenated, twinned and detwinned samples along the a and b axes to shade light on this issue. We were able to measure the electrical and thermal conductivity using the same contacts and hence determine the Lorenz number L = $ kappa$p/T accurately.<br>Attributing the normal state anisotropy in the heat transport to electrons in the Cu-O chains, the Lorenz number takes on its full Sommerfeld value i.e. $L = L sb0.$ Under this assumption, the phonon conduction is about the same in the superconducting and deoxygenated samples.<br>Our results are discussed in connection with the two possible mechanisms for heat conduction in the superconducting state. We find that although a strong case can be made for the "electronic scenario" whereby the peak is due to rapidly increasing electron mean free path below $T sb{c},$ it is still not compelling at this stage.<br>In addition, it is found that the thermal conductivity along the a and b axes is isotropic at low temperatures, with a nonzero linear term in $ kappa,$ indicative of some uncondensed electrons as $T rightarrow$ 0. This low temperature isotropy contradicts previous explanations in terms of non-superconducting chains.

<p>High-temperature superconductors have been intensely studiedsince the discovery, almost 20 years ago. Their layeredstructure, extreme type-II behavior, large anisotropy, andstrong fluctuations have led to a large number of new andinteresting problems. In this work the resistive transitionhave been studied in YBa₂Cu₃O_7-δsingle crystals, from the superconductingfluctuations above T<i>c</i>down to the vortex matter near the onset of resistivity.Superconducting fluctuations above T<i>c</i>are suitably studied by measuring themagnetoconductivity Δσ = 1/ρ(B)-1/ρ(0).Such experiments were performed on untwinned, optimally dopedsamples, for<b>I</b>||<b>ab</b>. For<b>H</b>||<b>c</b>, fluctuations in the CuO-chains was not important, andfluctuations in the CuO2 planes seemed isotropic. The in-planecoherence length anisotropy was determined to be close tounity. For<b>H</b>||<b>ab</b>, Δσ<i>b</i>depended on the field direction, indicating an effect ofthe chains on the magnetoconductivity in thisconfiguration.</p><p>The nature of the vortex phase below T<i>c</i>can be examined through vortex-correlation measurements.Using a modified pseudo-flux transformer (PFT) geometry forin-plane experiments, the magnetic field could be appliedparallel to both the a, b, and c axis. A strong Lorentz forcewas detected, and observed to be a requirement for the meltingstep feature. The resistive anisotropy close to T<i>c</i>was strongly field and temperature dependent, which wasexplained by an almost isotropic fluctuation contribution.</p><p>The effect of anisotropy on vortex-liquid correlation infields<b>H</b>||<b>ab</b>, was studied by<i>c</i>-axis transport measurements in oxygen-deficientsamples, using a PFT configuration. Increasing disordersuppressed both longitudinal and transverse correlation. Inheavily underdoped samples, vortex correlation was enhanced formagnetic fields exactly aligned with the<i>ab</i>plane because of the strong anisotropy. Also, thesolid-to-liquid transition temperature became nearly fieldindependent.</p><p>Attempts were also made to connect the fluctuation regime ofthe resistive transition with the vortex region,by accountingfor critical fluctuations close to the transition.</p><p><b>Keywords:</b>high-temperature superconductors, YBa₂Cu₃O_7-δ, untwinned YBCO, oxygen deficiency,superconducting fluctuations, magnetoconductivity, in-planeanisotropy, vortex liquid, vortex solid, vortex correlation</p>

Thin films of the high-T<SUB>c</SUB> superconductor YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-x</SUB> (YBCO) are the key to devices that function at the temperature of liquid nitrogen. The main priority in depositing YBCO films is the ability to deposit smooth epitaxial films with the desired crystal structure and the correct level of oxygenation. This thesis describes the crystal structure, composition and initial growth stages of YBCO films prepared by planar dc high pressure sputtering. X-ray diffraction (XRD), atomic force microscopy (AFM), and electrical measurements have been used to study the films. Prior to a description of these experiments, two preliminary chapters are included in this thesis. The first chapter is an introduction to some basic concepts of superconductivity, and the crystal structure as well as the physical properties of YBCO. The second chapter reviews important issues and compares the different deposition techniques for preparing YBCO thin films. In a preliminary study of YBCO films deposited under different PxD conditions (the product of pressure and target-to-substrate distance), it was found that a PxD of 2000 Pa-mm is necessary to prevent preferential resputtering. A study of the thermalisation of the high energy particles emanating from a sputtering target was carried out on both Nb films and YBCO films. The sputtering atmospheres and the time for which the ceramic YBCO target has been operated under such atmosphere was found to influence the superconducting critical temperatures of sputtered YBCO films. The effect of oxygenation of the target surface on the superconducting properties of films deposited was studied with various amounts of hydrogen gas added to the sputtering gas or residual water vapour in the vacuum system. The initial stages of YBCO films grown on SrTiO<SUB>3</SUB> substrates were investigated with different film thickness. For the 1-nm-thick film flat island nuclei with one-unit-cell height were found using AFM which is consistent with the observation by XRD. Secondary phases were found to appear in the 2-nm-thick film. The effect of secondary phase precipitates on the superconducting properties and surface morphology of the films is discussed. Spiral growths were found to appear in films with thicknesses larger than 24nm, and their origin is discussed. To study the effect of substrate lattice misfit on the initial stages of film growth, NdGaO<SUB>3</SUB> substrates were chosen.

Ce mémoire décrit mes travaux de recherche depuis le début de ma thèse de doctorat en<br />octobre 1993. J'ai principalement travaillé sur deux types d'oxydes: YBCO et LSMO. J'ai toujours<br />cherché à aborder le développement des microdispositifs dans leur ensemble, c'est à dire de la<br />couche mince à la caractérisation du composant. Une partie de mon travail a concerné l'étude des<br />propriétés structurales, électriques ou magnétiques des couches minces afin d'optimiser et stabiliser<br />les conditions de dépôts optimales. Les deux oxydes YBCO et LSMO présentent une structure de<br />type pérowskite et nécessitent des conditions de dépôts similaires (température de l'ordre de 700-<br />750 °C dans une atmosphère oxygénée). J'ai utilisé trois méthodes de dépôt différentes: l'ablation<br />laser pulsée, la pulvérisation cathodique DC on axis sous haute pression et la pulvérisation<br />cathodique RF off axis.

For cost-efficient power applications of superconducting coated conductors based on YBa\(_2\)Cu\(_3\)O\(_7\) (YBCO) films, in applied fields or in self-field, further improvement of critical current by artificial flux pinning centres is required. This project investigated the increase in critical current density (J\(_c\)) and related physical properties of YBCO films by self-assembling nanotechnology of pinning centres, using substrate decoration, quasi-multilayers (using noble metals and Pr\(_2\)Cu\(_3\)O\(_7\) (PBCO) in both cases), and targets containing BaZrO\(_3\) (BZO) nano-inclusions. Samples were prepared by pulsed laser deposition (PLD) on single crystal SrTiO\(_3\) (STO) substrates and on Ni-W Rolling-Assisted Biaxially Textured Substrates (RABiTS). Optical lithography and chemical etching were used to prepare samples for transport measurements. The superconducting properties were characterised by AC susceptibility, magnetisation loops and transport measurements using a Magnetic Property Measurement System (MPMS) and a Physical Properties Measurement System (PPMS). Scanning and Transmission Electron Microscopy (SEM) and (TEM), Atomic Force Microscopy (AFM) and X-ray diffraction were also used to characterise the micro-structure of the films and the structure of artificially-induced pinning centres. The optimum conditions for the growth of YBCO films, Ag and PBCO nano-dots, and BZO nano-columns were investigated. Combinations of all three nana-structuring approaches resulted in a maximum J\(_c\) in applied fields and self-field. The related physical properties such as angular dependence of J\(_c\), vortex melting line, pinning force, frequency dependence of J\(_c\), were also investigated to understand pinning mechanisms in the films. The combination of Ag nano-dots and BZO nano-inclusions in the YBCO target provided the greatest improvement of critical currents of the film in applied fields.

This thesis deals with the transport properties and critical current limitations found in YBa2Cu3O7[-delta] coated conductors prepared by the &amp;quot;rolling assisted biaxially textured substrate&amp;quot; (RABiTS) approach. For this purpose a buffer layer system composed of CeO2 and yttria-stabilised zirconia, and subsequently a YBa2Cu3O7[-delta] film were epitaxially grown by pulsed laser deposition on a biaxially textured metallic substrate. The resulting texture of the YBa2Cu3O7[-delta] film is crucial for the achievement of high critical current densities. A propagation of the granular structure of the metallic substrate into the YBa2Cu3O7[-delta] film was detected, which leads to the formation of a YBa2Cu3O7[-delta] grain boundary network and limits the critical current density of the samples. In order to study this limitation, critical current measurements were performed on the prepared samples at different temperatures and magnetic fields, detecting a transition between intergrain and intragrain current limitation that occurs at the so-called crossover magnetic field. The crossover magnetic field was found to shift to lower values as the temperature was increased. It was concluded that the grain boundary network limits the critical current density of the YBa2Cu3O7[-delta] coated conductor only for magnetic fields below the crossover field.<br>In der vorliegenden Dissertation werden Transporteigenschaften und die Limitierung der kritischen Stromdichte von YBa2Cu3O7[-delta] Bandleitern untersucht. Für die Präparation wird das epitaktische Schichtwachstum auf biaxial texturierten Substraten genutzt (RABiTS-Technik). Dabei wird mittels gepulster Laserdeposition eine Pufferschicht aus CeO2 und Yttrium-stabilisiertem Zirkonoxyd (YSZ) und anschließend eine YBa2Cu3O7[-delta] Schicht epitaktisch auf ein Substrat aufgebracht. Die resultierende biaxiale Textur der YBa2Cu3O7[-delta]-Schicht spielt eine Hauptrolle, um möglichst hohe Stromdichten zu erreichen. Es zeigte sich, daß die granulare Struktur des Substrates in die YBa2Cu3O7[-delta]-Schicht übertragen wird und zur Ausbildung eines Korngrenzennetzwerkes führt, welches wiederum die zu erwartende kritische Stromdichte begrenzt. Um die Wirkung des Korngrenzennetzwerkes zu untersuchen, wurden kritische Ströme der gewachsenen Schichten in Abhängigkeit der Temperatur und des angelegten Magnetfeldes gemessen. Es stellte sich heraus, daß die Limitierung des Stroms bei schwachen Magnetfeldern zwischen den einzelnen Körnern bestimmend ist, die dann bei größeren Feldern einer Strombegrenzung innerhalb der Körner weicht. Das beide Bereiche trennende Magnetfeld wird als Übergangsfeld bezeichnet. Daraus kann geschlußfolgert werden, daß das Korngrenzennetzwerk von YBa2Cu3O7[-delta] Bandleitern den Strom nur für magnetische Felder unterhalb des Übergangsfeldes begrenzt.

Orientador: Sergio Gama<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin<br>Made available in DSpace on 2018-07-14T01:26:16Z (GMT). No. of bitstreams: 1 Jardim_RenatodeFigueiredo_D.pdf: 11537351 bytes, checksum: 83bdd9cb2096cd89f2952ee81d958daf (MD5) Previous issue date: 1989<br>Resumo: Amostras de YBa2(Cu1-xMnx)3O7-d , x = 0,0, 0,01, 0,025, 0,05, 0,075, 0,10, 0,15 e 0,20, foram sintetizadas às temperaturas de 950º, 970º e 1020º C. As amostras foram caracterizadas por difração de raios ¿ X, metalografia óptica, resistividade elétrica e susceptibilidade magnética. Supercondutividade ao redor de 92 K foi observada para todas as amostras. O limite de solubilidade do Mn no composto YBa2Cu3O7-d é muito baixo, menor que x = 0,005. Isto implica em precipitação de fases adicionais não supercondutoras e de estequiometrias Y2BaCuO5 e Ba3Mn2O8. A precipitação destas fases altera substancialmente a microestrutura dos compostos, fato este observado principalmente na série de 970º C. Para esta série foi observada uma anomalia induzida pela microestrutura nas propriedades de transporte de calor<br>Abstract: Samples of the compounds YBa2(Cu1-xMnx)3O7-d , x = 0,0, 0,01, 0,025, 0,05, 0,075, 0,10, 0,15 e 0,20, were sintered at. 950º, 970º e 1020º C. These samples were characterized by X ¿ ray diffraction, optical metallography, electrical resistivity and magnetic susceptibility. Superconductivity around 92 K for all samples. The YBa2Cu3O7-d solubility limit for Mn is very small, less than x = 0,005. This fact means precipitation of non-superconducting additional phases, whose stoichiometric were identified as Y2BaCuO5 and Ba3Mn2O8. The presence of this phases changes substancially the microstructure of the samples. This effect being greater for the samples sintered at 970º C. For this series of samples it was observed na anomaly in the thermal transport properties induced by the microstructural modifications<br>Doutorado<br>Física<br>Doutor em Ciências

En el presente trabajo se reporta la fabricación, mediante la ruta Sol-Gel, de capas superconductoras de YBCO depositadas sobre sustrato de YSZ mediante Deposición de Solución Química y cristalizadas con tratamientos térmicos de Calcinado y Sinterizado, siendo este último en ambiente oxidante y re-oxigenada la muestra. La caracterización cristalográfica es obtenida mediante el uso de la técnica de Difracción de Rayos-X, observándose picos intensos y bien definidos en la dirección (00l), los cuales son propios de la fase Superconductora así como la presencia de fases secundarias como la llamada Fase Verde Y2BaCuO5 en menor intensidad. Posteriormente se realizó una primera medida de Susceptibilidad Magnética en los modos Zero Field Cooling (ZFC) y Field Cooling (FC) a campo externo de 100 Oe a fin de observar el carácter superconductor de la muestra, de donde se obtiene una Temperatura Crítica Superconductora de 90K. La morfología superficial de la muestra fue estudiada a través de Microscopía óptica, observándose claramente la presencia de la Fase Verde, lo cual se confirma con DRX, además de observar que se obtuvo un filme granular. Mapeos EDX permiten observar la disposición de los elementos Y, Ba, Cu, O, Zr que componen la muestra. Se estudia la rugosidad de la película mediante Microscopía de Fuerza Atómica, obteniéndose el valor de la rugosidad RMS equivalente a 0,2939μm además de una Media de Rugosidad de 0,2197μm. Para el estudio de la textura fuera-del-plano en las capas de YBCO se realiza el cálculo del índice de textura, cuyo valor es 0,91. Posteriormente medidas ω-scan alrededor de la reflexión (005) dan cuenta de la presencia de 3 regiones granulares de YBCO a diferentes grados de textura: 0,4°, 6,0° y 9,0° (Δω). Finalmente se realizan mediciones de Susceptibilidad magnética a campo externo de 50, 100, 300 y 500 Oe en disposición del campo magnético externo aplicado tanto paralelo como perpendicular al sustrato, lográndose evidenciar una diferencia en la respuesta del filme según la orientación del campo, lo cual confirma una anisotropía magnética producto del ordenamiento epitaxial. Finalmente, se realiza una comparación de capas de YBCO crecidas sobre sustratos de SrTiO3, LaAlO3 y YSZ, en todas ellas utilizando la misma ruta de fabricación.<br>Tesis

We have used thermal conductivity measurements at low temperature to probe the behavior of the unconventional superconductor YBa2Cu 3O7-delta (YBCO). Two aspects were investigated: (1) the in-plane anisotropy, studied in order to gain insight into the contribution of CuO chains, and (2) the effect of a magnetic field, investigated in order to explore the contribution of vortices. Our results on the low temperature thermal conductivity are in good quantitative agreement with the theory for a d-wave superconductor. We have found a very weak (or even negligible) anisotropy suggesting that the anisotropy could not simply be explained by mass tensor anisotropy or the plasma frequency anisotropy. The magnetic field studies revealed an increase in the residual linear term (kappa/ T as T &rarr; 0) with field, reflecting the contribution to the density of states from the extended quasiparticles due to their Doppler shift in the presence of vortices. These results are in good quantitative agreement with the theoretical predictions.

Ce travail decrit la realisation et la mise en forme du supraconducteur haute temperature yba#2cu#3o#7##x par la technique sol-gel. Cette technique permet d'acceder a des materiaux de formes variees: ceramiques massives, films, fibres. Elle ouvre la possibilite d'obtenir un materiau plus homogene a plus basse temperature. Quatre voies de syntheses ont ete utilisees: acetates, acetates/a. P. A. Nitrates/a. P. A. Et alcoxydes/b-dicetonate. La voie nitrates/a. P. A. A permis la synthese d'une poudre submicronique (0. 7 micron) exempte de phases secondaires. Les ceramiques massives ont ete elaborees suivant deux protocoles experimentaux, avec et sans ajout de liant organique. Nous avons mis en evidence que cet ajout permettait une meilleure densification au detriment de la purete et de la stoechiometrie en oxygene. Les resultats electriques des films realises sur differents substrats font apparaitre une degradation de la phase supraconductrice due a la reactivite de la phase 123 avec les substrats. En modulant la viscosite des gels de nitrates/a. P. A. Et d'acetates/a. P. A. Nous avons etire des fibres. Les caracteristiques electriques demontrent la potentialite de la methode dans l'elaboration de fibres supraconductrices

Critical currents in the latest biaxially textured 'coated conductors' are now limited by 2D networks of low angle grain boundaries (LAGBs) with misorientation θm = 1 - 10°. In order to understand and optimise current transfer in these materials it is essential to elucidate the electromagnetic behaviour of the LAGB. This work presents an investigation into the transport properties of [001]-tilt LAGBs formed by the thin film deposition of YBa2Cu3O7 onto bicrystalline substrates. Through the use of a precision two-axis goniometer, measurements of the V-I characteristic and critical current density were made as magnetic field was rotated in angles θ and φ relative to the LAGB defect. It is found that for fields applied parallel to the LAGB defect plane, dissipation is dominated by the viscous flux flow of vortices along the boundary. Clear evidence for this is found in the V-I characteristic, which displays an increased linearity indicative of the viscous regime. It is shown that the number of vortex rows involved in the flow process can discontinuously switch, leading to a V-I characteristic made up of straight segments of different gradient. For fields applied away from the LAGB defect plane a kinked vortex structure develops and the boundary critical current density, JcGB, is determined by the channelling of vortex segments still lying within the LAGB. The channelling regime is seen in angular measurements as a marked decrease in JcGB(θ,φ) as field becomes aligned to within critical angles φK or θK of the LAGB. The aligned vortices experience a reduction in dimensionality that is manifest in a reduced temperature dependence of JcGB(T). For fields applied at a sufficiently large angle from the defect plane the deleterious effects of the LAGB on current transport are mitigated considerably. In this regime a collinear vortex structure is regained and transport is controlled by the intragranular (IG) sections of the LAGB track; JcGB = δJcIG where δ ~ 0.8, a result that is independent of field, temperature and angle for a 4.9° LAGB. For rotation of the applied field within the LAGB defect plane, the presence of a pinning peak in JcGB for field aligned to the dislocation array is confirmed and modelled. The peak is found to be absent in IG track measurements and increases relative to the intrinsic peak with both increasing field and temperature. In addition, a pronounced angular hysteresis is presented, which is directly linked to a corresponding 'static' hysteresis in JcGB(B) with field. Magneto-optic measurements confirm that this effect is controlled by the flux density profile in the IG regions of the LAGB track. Finally, above a temperature, angle and sample dependent merging field, B*, the LAGB is found to be effectively transparent, as δ ~ 1. This is due to the irreversibility line, above which dissipation occurs across the whole LAGB track.

A coated conductor is generally fabricated by depositing a high Tc superconducting layer onto a flexible metallic substrate, using intermediate buffer layers to prevent chemical interaction. In order for the superconductor to be capable of carrying a high current density, its grains must have good crystallographic alignment in order to avoid the presence of high angle grain boundaries. This can be ensured by transferring the texture from the substrate through epitaxial film growth. The main substrate considered in this thesis is a Ni-Fe alloy. When cold-rolled, NiFe develops a preferential orientation and upon annealing at an elevated temperature, undergoes primary recrystallisation to form grains with the cube texture {100}<001>. There crystallisation process and the texture of the tapes has been examined and various buffer layers have been fabricated. As silver does not react adversely with high temperature superconductors, it has been deposited onto Pd-buffered NiFe by DC sputtering and very sharp cube texture is obtained. Ceramic buffer layers, CeO2 and YSZ, have been deposited by RF sputtering, though an undesirable (111) oriented component accompanies the cube textured material. Also a technique has been developed to produce a suitably oriented native oxide of NiFe by a simple oxidation technique. Preliminary attempts to deposit YBCO films onto these buffer layers have shown that the quality of the metallic buffers is degraded by rapid inter-diffusion at elevated temperatures, but that cube textured material can be deposited on the oxide buffer layers. The percolative nature of current flow in such coated conductors has been considered through the development of a grain network model. As the texture of the superconducting layer is directly influenced by the underlying layers, measurements from the substrate and buffer layers are applied in order to model the orientations of the grains in a superconducting overlayer. The model calculates the critical current of coated conductors as a function of parameters such as length, width, grain size and texture, as well as examining factors such as cracks and highly misoriented grains.

Los esfuerzos por realizar nuevos descubrimientos en el campo de la superconductividad están motivados por una imperiosa necesidad de su aplicación en el día a día.[1-7] En este sentido, la fabricación de cables superconductores de grandes dimensiones ha sido posible gracias a la inclusión de resultados obtenidos en laboratorios trabajando con sistemas modélicos,[8-12] donde los objetivos se centran en la mejora de las prestaciones del YBa2Cu3O7, uno de los materiales con mejores resultados en aplicación. La inhibición del movimiento colectivo de la red de vórtices, efecto generador de la disipación de energía en cables superconductores, ha sido uno de los frentes más atacados para la optimización de resultados. La estructuración de la red de vórtices por parte de defectos en el material es un muy buen indicador de la interacción presente entre vórtices y defectos, interacción necesaria para la inhibición del movimiento de la red de vórtices y por consiguiente para la mejora de las prestaciones de los materiales superconductores. Sin embargo las técnicas para la evaluación de los resultados obtenidos trabajan con la respuesta colectiva de la red[13,14] obteniendo resultados que no permiten discernir fácilmente entre los diferentes aportes a la inhibición de movimiento de la red de vórtices. En este marco, el trabajo de tesis aquí plasmado estudia la estructuración de la red de vórtices debido a la presencia de defectos, permitiendo una comparación cuantitativa entre defectos de diferente naturaleza. Dicho análisis se centra en la respuesta del YBa2Cu3O7 ante la presencia de defectos artificiales superficiales capaces de mejorar las propiedades del material superconductor. El estudio se lleva a cabo visualizando la red de vórtices mediante la técnica de decoración magnética en sistemas modélicos (monocristales y películas de YBa2Cu3O7 crecidos respectivamente por los métodos de flujo y de epitaxialidad en fase líquida sobre sustratos de MgO). Los defectos artificiales estudiados son generado por dos técnicas diferentes, la irradiación con haz de iones focalizado y la indentación a escala nanométrica. Para la realización de dicho estudio primeramente se lleva a cabo el montaje y puesta a punto de la técnica de visualización empleada, la decoración magnética. Luego, a partir de los resultados de visualización de la red de vórtices obtenidos, se genera un modelo para la estimación de energías asociadas a la red. Este modelo permite discernir la contribución a la inhibición del movimiento de la red por parte de diferentes tipos de defectos, comparando por primera vez de manera cuantitativa resultados de este tipo. Finalmente se realiza el modelado de sistemas virtuales, lo que permite estimar propiedades de los defectos a partir de una comparación directa entre sistemas de vórtices reales y artificiales. Notamos que este trabajo demuestra avances en tres frentes importantes. Por un lado hemos puesto en marcha una técnica de visualización de dominios magnéticos (aplicada aquí exclusivamente al estudio de vórtices en materiales superconductores). Esta técnica está presente solo en media docena de laboratorios en el mundo. Por otra parte hemos generado una herramienta de fácil aplicación para el estudio cuantitativo de las energías asociadas al anclaje de vórtices (modelo para la determinación de energías en la red de vórtices). La misma ha demostrado ser muy dócil en cuanto a ámbito de aplicación se refiere, permitiendo trabajar en diferentes materiales observados por decoración y demostrando sus posibilidades trabajando incluso en sistemas artificialmente generados. Las hipótesis consideradas para la generación de este modelo fueron comprobadas mediante el modelado de sistemas virtuales, afianzando dicho modelo energético y permitiendo a su vez caracterizar los defectos artificiales generados en el propio material YBa2Cu3O7. Por último se realizó un avance muy importante en relación a la naturaleza de los centros de anclaje de vórtice artificiales, logrando comparar de manera cuantitativa las fuerzas de anclaje asociadas a las diferentes técnicas empleadas en la generación de los mismos. Dicho análisis, realizado precisamente en YBa2Cu3O7, es extensible al ámbito de cintas superconductoras o dispositivos electrónicos, entre otros. Mostramos aquí un trabajo que nace de la necesidad de un estudio comparativo claro entre resultados de interacción vórtice-defecto asociados a diferentes tipos de defectos. Un trabajo que involucra desde la construcción y puesta en marcha del sistema empleado para la obtención de resultados hasta el análisis de los mismos generando herramientas para tal efecto, incluyendo un estudio final mediante el modelado virtual de los propios sistemas medidos experimentalmente. Un trabajo que demostramos es, tanto en parte como en conjunto, de fácil aplicación al estudio de materiales superconductores; innovando en el análisis de resultados propuesto así como aportando una nueva técnica al laboratorio. [1] T. G. Holesinger, L. Civale, B. Maiorov, D. M. Feldmann, J. Y. Coulter, D. J. Miller, V. A. Maroni, Z. Chen, D. C. Larbalestier, R. Feenstra, X. Li, Y. Huang, T. Kodenkandath, W. Zhang, M. W. Rupich y A. P. Malozemoff, Advanced Materials, 20, 391 (2008). [2] S. R. Foltyn, L. Civale, J. L. MacManus-Driscoll, Q. X. Jia, B. Maiorov, H. Wang y M. Maley, Nature Materials, 6, 631 (2007). [3] Y. Iijima, N. Tanabe, O. Kohno y Y. Ikeno, Appl. Phys. Lett., 60, 769 (1992). [4] X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter y D. E. Peterson, Appl. Phys. Lett., 65, 1961 (1994). [5] D. P. Norton, A. Goyal, J. D. Budai, D. K. Christen, D. M. Kroeger, E. D. Specht, Q. He, B. Saffian, M. Paranthaman, C. E. Klabunde, D. F. Lee, B. C. Sales y F. A. List, Science, 274, 755 (1996). [6] Y. Kamihara, H. Hiramatsu, M. Hirano, R. Kawamura, H. Yanagi, T. Kamiya y H. Hosono, J. Am. Chem. Soc., 128, 10012 (2006). [7] Y. Kamihara, T. Watanabe, M. Hirano y H. Hosono, J. Am. Chem. Soc., 130, 3296 (2008). [8] N. Roma, S. Morlens, S. Ricart, K. Zalamova, J. M. Moreto, A. Pomar, T. Puig y X. Obradors, Superconductor Science and Technology, 19, 521 (2006). [9] S. Morlens, N. Romá, S. Ricart, A. Pomar, T. Puig y X. Obradors, Journal of Materials Research, 22, 2330 (2007). [10] A. Hassini, A. Pomar, C. Moreno, A. Ruyter, N. Roma, T. Puig y X. Obradors, Physica C: Superconductivity, 460-462, 1357 (2007). [11] M. Gibert, T. Puig y X. Obradors, Surface Science, 601, 2680 (2007). [12] J. Gutierrez, A. Llordés, J. Gázquez, M. Gibert, N. Romà, S. Ricart, A. Pomar, F. Sandiumenge, N. Mestres, T. Puig y X. Obradors, Nature Materials, 6, 367 (2007). [13] J. Gutierrez, T. Puig y X. Obradors, Applied Physics Letters, 90, 162514 (2007). [14] A. Palau, T. Puig, X. Obradors y C. Jooss, Phys. Rev. B, 75, 054517 (2007).<br>Efforts in superconductivity for new discoveries are pushed up for a vital necessity of application.[1-7] It is know that construction of long superconductor cables have been able due to application of results obtained in lab experiments using YBa2Cu3O7 model systems,[8-12] superconductor material with the best performance. Vortex pinning has been the hot topic for improve superconductor properties, since this effect is the one that produce loose of energy. Vortex lattice structured due to material defects presence point out a vortex-defect interaction necessary for a good vortex pinning and, in consequence, an improvement of superconductor properties. However, evaluation techniques typically used work with the collective behavior of the vortex lattice,[13, 14] with results that barely allow to separate individual contributions from different interactions. This thesis is focused on the vortex lattice structured analysis due to defect presence, allowing a quantitative comparison between different kinds of defects. The analysis is based on the YBa2Cu3O7 flux line lattice behavior in direct interaction with surface artificial defects that can improve superconductor properties of the material. The study uses the Magnetic Decoration technique for the visualization of the flux line lattice in model systems (single crystals and films of YBa2Cu3O7 growth respectively by flux method and liquid phase ephitaxy on MgO substrates). Artificial defects under study are generated using two different techniques, focused ion beam and indentation at nanometric scale. For this study, first of all a montage and set up of the magnetic decoration technique is doing. Then a model for flux line lattice energies estimation is developed based on magnetic decoration results. This model allows evaluating separately individual pinning contributions, comparing for the first time results in a quantitative way. Finally a virtual systems modeling is performed, estimating defect properties due to a direct comparison between real and artificial vortex systems. We point out that this work shows highlights in three different ways. In one hand we have started with a technique for magnetic domains visualization (here used exclusively for vortices in superconductor materials). This technique is present in just a few laboratories all around the world. At the other hand we have generated an easy tool for a quantitative study of pinning energies (model for energy identification at flux line lattice). This tool has been able to work very well at different conditions, giving results for several materials and even for artificially generated vortex systems. Hypothesis considered to the formulation of this model were probed through modeling of virtual systems, supporting the energy model and allowing also defect characterization artificially generated at the YBa2Cu3O7 material. Finally we have carried out an important develop about nature of pinning due to artificial defects, comparing in a quantitative way results associated to different artificial defect generation techniques. This analysis performed in YBa2Cu3O7, is applicable to a broad range of materials as well as topics (e.g. coated conductors, electronic devices, etc.). Here we show a work based on a simple but strong necessity of a clear comparative study between vortex-defect interactions associated to different kind of defects. A work that involves from construction of experimental technique in use to the generation of a tool for the corresponding result analysis, including a final study modeling virtually the systems of vortices experimentally observed. A work that was shown, in part as well as in a complete route, easily applicable to superconductor materials, developing new analysis routes and also establishing a new technique at the laboratory. [1] T. G. Holesinger, L. Civale, B. Maiorov, D. M. Feldmann, J. Y. Coulter, D. J. Miller, V. A. Maroni, Z. Chen, D. C. Larbalestier, R. Feenstra, X. Li, Y. Huang, T. Kodenkandath, W. Zhang, M. W. Rupich and A. P. Malozemoff, Advanced Materials, 20, 391 (2008). [2] S. R. Foltyn, L. Civale, J. L. MacManus-Driscoll, Q. X. Jia, B. Maiorov, H. Wang and M. Maley, Nature Materials, 6, 631 (2007). [3] Y. Iijima, N. Tanabe, O. Kohno and Y. Ikeno, Appl. Phys. Lett., 60, 769 (1992). [4] X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter and D. E. Peterson, Appl. Phys. Lett., 65, 1961 (1994). [5] D. P. Norton, A. Goyal, J. D. Budai, D. K. Christen, D. M. Kroeger, E. D. Specht, Q. He, B. Saffian, M. Paranthaman, C. E. Klabunde, D. F. Lee, B. C. Sales and F. A. List, Science, 274, 755 (1996). [6] Y. Kamihara, H. Hiramatsu, M. Hirano, R. Kawamura, H. Yanagi, T. Kamiya and H. Hosono, J. Am. Chem. Soc., 128, 10012 (2006). [7] Y. Kamihara, T. Watanabe, M. Hirano and H. Hosono, J. Am. Chem. Soc., 130, 3296 (2008). [8] N. Roma, S. Morlens, S. Ricart, K. Zalamova, J. M. Moreto, A. Pomar, T. Puig and X. Obradors, Superconductor Science and Technology, 19, 521 (2006). [9] S. Morlens, N. Romá, S. Ricart, A. Pomar, T. Puig and X. Obradors, Journal of Materials Research, 22, 2330 (2007). [10] A. Hassini, A. Pomar, C. Moreno, A. Ruyter, N. Roma, T. Puig and X. Obradors, Physica C: Superconductivity, 460-462, 1357 (2007). [11] M. Gibert, T. Puig and X. Obradors, Surface Science, 601, 2680 (2007). [12] J. Gutierrez, A. Llordés, J. Gázquez, M. Gibert, N. Romà, S. Ricart, A. Pomar, F. Sandiumenge, N. Mestres, T. Puig and X. Obradors, Nature Materials, 6, 367 (2007). [13] J. Gutierrez, T. Puig and X. Obradors, Applied Physics Letters, 90, 162514 (2007). [14] A. Palau, T. Puig, X. Obradors and C. Jooss, Phys. Rev. B, 75, 054517 (2007).

A high critical current density Jc is crucial for the application of HTS YBa2Cu3O7-δ (YBCO) in the fabrication of energy efficient power devices and wires. We have prepared and studied YBCO films with nanoinclusions for increasing the current-carrying capability. All films were prepared by pulsed laser deposition (PLD) on single crystal SrTiO3 (STO) substrates at optimised condition parameters. We found that the substrate temperature Ts of 780° C, laser energy E ~ 218 mJ/pulses, distance between target and substrate Dt of about 55 mm, annealing oxygen pressure Oap 450 Torr and cooling rate Ct 8°/min were the optimum conditions for making good films with Tc = 91 K. We have used a method for introducing artificial pinning centers which has been shown to be successful in the nanotechnology of pinning centres: distributing a secondary phase, YBCO with 1% Gd2Ba4CuWOy (2411W) nano-inclusions, YBCO with 2% wt BaZrO3 (BZO) and YBCO with 4% wt BZO nano-crystalline particles in the film. The superconducting properties were determined by AC susceptibility, magnetisation loops and transport measurements using a Quantum Design Magnetic property measurement system (MPMS) and a Physical properties measurement system (PPMS). Scanning and transmission electron microscopy (SEM) and (TEM), Atomic force microscopy (AFM) and X-ray were also used to characterise the micro-structure of the films. Both 2411W and BZO nano-inclusions led to increased Jc in applied fields and self-field. Scaling of the flux pinning force based on the Dew-Hughes model has been used in this work for investigating the flux pinning mechanism.

La plasticite d'echantillons massifs de yba#2cu#3o#7##x elabores par frittage a ete etudiee par fluage a haute temperature (650c-900c) sous pression partielle d'oxygene variable 10 pa <po#2<10#5 pa. Les microstructures de deformation ont ete caracterisees par microscopie electronique a transmission. L'unique plan de glissement mis en evidence est du type <100> (001). La contribution de la precipitation de cuo dans une matrice 1-2-3 ou sur les dislocations, a ete discutee