Fabrication of nanoscale Josephson junctions and Superconducting Quantum Interference Devices (SQUID) is very promising but challenging topic in the superconducting electronics and device technology. In order to achieve best sensitivity of SQUIDs and to reproduce them easily with a straightforward method, new fabrication techniques for realization of nanoSQUIDs needs to be investigated. This study concentrates on investigation of new fabrication methodology for manufacturing nanoSQUIDs with High Temperature Bi-Crystal Grain Boundary Josephson Junctions fabricated onto SrTiO3 bi-crystal substrates using YBa2Cu3O7-δ (YBCO) thin-films. In this process nanoscale patterning of YBCO was realized by using electron beam patterning and physical dry etching of YBCO thin films on STO substrates. YBCO thin films were deposited using RF magnetron sputtering technique in the mixture of Ar and O2 gases and followed by annealing at high temperatures in O2 atmosphere. Structural characterization of YBCO thin films was done by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Superconducting properties of thin films was characterized by AC magnetic susceptibility measurements. Nanoscale structures on YBCO thin films were fabricated by one E-Beam Lithography (EBL) step followed by Reactive Ion Etching (RIE) and physical dry etching. First SiO2 thin film were deposited on YBCO by RF magnetron sputtering and it was patterned by EBL using Polystyrene (PS) as resist material and RIE. Then SiO2 was used as an etch mask for physical dry etching of YBCO and nanoscale structures on YBCO were formed.

The nonlinear electrodynamic characteristics and presence of vortex dynamics in pseudo 2-dimensional microbridges make them attractive to design novel passive and active microwave circuits. Before such applications could be feasibly accomplished, a greater understanding of the the these devices are necessary, by a complete DC, microwave and optoelectronic characterization. A cryostat design and construction is discussed including the creation of test beds for DC characterization. Coplanar waveguide (CPW) design methodology is presented and used for the creation of CPWs for microwave characterization. Microbridges and meander lines are also embedded into the CPWs for determining the microwave performance of said devices and for optoelectronic characterizations. Results are compared against accepted results from theory and simulations, introducing vortices as explanations for device behaviour. Feasibility of these devices as single photon detectors is discussed.

Dans ce mémoire, nous présentons le développement de détecteurs thermiques non refroidis de type pyroélectrique à base de films minces amorphes d'YBaCuO semi-conducteur pour des applications en imagerie infrarouge et térahertz. En première partie, nous étudions la composition et les propriétés optiques des films d'YBaCuO semi-conducteur. Nous avons montré par XPS l'existence d'un mélange entre plusieurs phases et nous avons déterminé la composition de la couche de contamination en surface d'YBaCuO, ainsi que le travail de sortie d'YBaCuO par UPS. Nous avons extrait l'indice de réfraction et le coefficient d'absorption sur une gamme de longueur d'ondes allant de l'ultraviolet à l'infrarouge proche ; nous avons aussi déterminé les valeurs des gaps optiques que nous avons corrélés à la structure granulaire des films d'YBaCuO. En seconde partie, nous étudions le comportement en transport électrique et la réponse optique de détecteurs pyroélectriques fabriqués à partir de ces films d'YBaCuO semi-conducteur. Le contact électrique entre YBaCuO et les plots métalliques peut être ohmique ou redresseur. Des mesures de résistivité en fonction de la température ont montré que la conduction électrique s'opère préférentiellement par sauts à distance variable des porteurs autour du niveau de Fermi. Les réponses à température ambiante des détecteurs dans l'infrarouge proche ont révélé - en fonction de la fréquence de modulation - un comportement de type passe-bande attribué à l'effet pyroélectrique, qui a pu être interprété par un modèle analytique. Les performances en termes de détectivité (1E9 cm.Hz^0,5/W) et de constante de temps (quelques microsecondes) se situent à l'état de l'art. / In this manuscript, we are presenting the development of uncooled thermal sensors of the pyroelectric type, based on thin films of amorphous YBaCuO semiconductor, for applications in terahertz and infrared imaging. In a first part, we discuss the composition and optical properties of the YBaCuO semiconducting films. By X-ray photoelectron spectroscopy, we show the existence of a mixture of several phases and deduce the composition of the YBaCuO surface contamination layer; by ultraviolet photoelectron spectroscopy, we determine the YBaCuO work function. By optical spectroscopy, we then extract the refractive index and the absorption coefficient over a range of wavelengths spanning from ultraviolet to the near infrared. We also determine the values of optical gaps that we have correlated with the granular structure of the YBaCuO films at the micro and nanoscales. In a second part, we study the electrical transport behavior and optical response of pyroelectric detectors made from these amorphous YBaCuO thin films. The electrical contact between YBaCuO and the metal connections can be ohmic as well as rectifying. Resistivity measurements as a function of temperature show that the electric conduction is preferentially dominated by variable distance hopping of the carriers around the Fermi level. The response of the sensors in the near infrared - as a function of the modulation frequency of the source - reveal at room temperature a band-pass type behavior attributed to the pyroelectric effect, which could be interpreted by an analytical model. The device performance in terms of detectivity (1E9 cm.Hz^0.5/W) and time constant (a few microseconds) are at the state of the art.

Orientador: Prof. Dr. Alexandre José de Castro Lanfredi / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016. / Este trabalho tem como objetivo o desenvolvimento de uma rota de sintese de nanofios supercondutores de alta temperatura critica de YBa2Cu3O7- (delta) pelo metodo de preenchimento de poro utilizando processo sol-gel. A preparacao do sol-gel foi realizada utilizando acetatos de itrio, bario e cobre como precursores e solubilizados em uma mistura de metanol, acido acetico e propanoico. O sol-gel foi depositado em membranas de policarbonato nanoporosas utilizadas como moldes para obtencao de amostras de nanofios. A fim de encontrar as condicoes de sintese, varios parametros foram estudados como a viscosidade da solucao precursora, temperatura e tempo de tratamento termico das amostras de nanofios de YBCO. Para esses estudos, as amostras foram caracterizadas por Microscopia Eletronica de Varredura (MEV), Difratometria de Raios X (DRX) e medidas de magnetizacao. Inicialmente, estudou-se o preenchimento da membrana porosa por sol-gel. Os nanofios de YBCO foram obtidos com a solucao precursora de viscosidade proxima a 100 mPa.s. Imagens de MEV mostraram a morfologia de nanofios com diametro da ordem de 100 nm. Estudos das condicoes de tratamento termico revelaram que as amostras de nanofios tratadas termicamente a temperatura de 800¿C por 4 h em atmosfera de oxigenio permitiu a obtencao de amostras de YBCO que mantiveram a morfologia nanofios. A formacao da fase ortorrombica do YBCO foi verificada por meio de difracao de raios X. Porem, a transicao supercondutora nessas amostras nao e bem definida e as propriedades magneticas sao menos intensas. Analises de DRX de amostras de nanofios tratadas termicamente a 800¿C por mais tempo, com patamar de oxigenacao a 400¿C, mostrou que ha presenca de fase YBa2Cu3O7-¿Â ortorrombica e de fases adicionais em maior proporcao. Isso tambem pode ser observado nas medidas magneticas dessas amostras. Por fim, resultados de difracao de raios X de amostras sinterizadas nas temperaturas de 850¿C e 900¿C por 4 horas em atmosfera de oxigenio revelaram a presenca predominante da fase YBCO. Ambas as amostras apresentaram a transicao supercondutora em Tc ~ 92 K na medida de magnetizacao versus temperatura. Porem, imagens de MEV dessas amostras revelaram que apenas aquela tratada termicamente a temperatura de 850¿C mantem a morfologia de nanofios com diametro medio de ~ 100 nm. Esta metodologia permitiu a obtencao de nanofios de YBCO, com caracteristicas estruturais e fisicas similares a obtida para o material na forma de bulk. / The aim of this work is to develop a synthetic route of high-Tc superconductor YBa2Cu3O7-ä nanowires by wet pore-filling method using sol-gel solution. Such sol-gel was prepared by yttrium, barium and copper acetates as precursors and solubilized in a mixture of methanol, acetic and propionic acids. The sol-gel solution was depositedon polycarbonate mesoporous membranes that were used as a template to obtain nanowire samples. In order to find an ideal synthesis condition, several synthesis parameters were studied, such as viscosity of precursor solution, temperature and time of heat treatment. Samples were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and magnetic measurements. Firstly, we have studied porous membrane filled by a sol-gel solution. The YBCO nanowires were obtained by precursor solution with viscosity of 100 mPa.s. Through SEM images it was verified the Y-Ba-Cu nanowire morphology with external diameter of 100 nm. Experimental studies of heat treatment conditions revealed that nanowire samples can be obtained by sintered temperature at 800°C during 4 hours in oxygen atmosphere. The orthorhombic YBCO crystallographic phase was identified by X-ray diffraction. However, it was detected considerable broadening in the superconducting transition samples and low intensities of magnetic proprieties. Furthermore, the nanowires sintered at 800°C during long time with oxygenation step at 400°C exhibited the presence of orthorhombic YBa2Cu3O7-ä crystallographic phase and presence of secondary phases in more quantities. The magnetic measurements confirmed the presence of secondary phases in sample. Finally, XRD results of sintered samples at temperature range 850-900°C for 4 hours in oxygen atmosphere exhibit YBCO as the major phase. The magnetic measurements showed that both samples exhibit superconducting transition at Tc ~ 92 K. However, SEM images indicated that only the sample sintered at 850°C present nanowire morphology with average diameter of 100 nm. This methodology allowed the production of YBCO nanowires with structural characteristics and physical properties similar to the bulk samples.

Orientadora: Profa. Dra. Marcia Tsuyama Escote / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016. / 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. / 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.

<div>In this research, the use of a Type-2 superconducting material (i.e. Yttrium Barium Copper Oxide) as a magnetic flux source within synchronous machines is considered. To do so, an analytical model is applied to predict the magnetic field and the currents that are induced within the material when it is magnetized to a mixed-state. These induced currents are then used to model the synchronous machine performance within a 2-dimensional Method of Moments (MoM) formulation. The MoM-based model is used in tandem with a thermal equivalent circuit to calculate the cooling required to keep the YBCO below its critical temperature. These are utilized within a genetic algorithm (GA) to evaluate the tradeoffs between mass and loss for several example electric drives ranging from 10 kW-20 MW. The expected mass and loss of the YBCO machines are compared to those of a standard permanent magnet synchronous machine (PMSM). Specifically, Pareto-optimal fronts are used to assess power levels where cryo-cooled YBCO materials may be warranted.<br></div>

In dieser Arbeit wurde die Kupferoxidebene des Hochtemperatur - Supraleiters Yttrium- Barium-Kupferoxid (YBa2Cu3O6+y) mit Hilfe von Kernmagnetischer-Resonanz (NMR - nucleus magnetic resonance) unter Drücken von bis zu 4.4GPa untersucht. Es wurden 2 dieser Druckzellen gebaut, sie enthielten verschieden stark dotierte Einkristalle. Die Änderungen der Ladungsverteilungen in der Kupferoxidebene abhängig von der Dotierung und vom Druck lagen hierbei im Fokus der Untersuchungen. Motivation dieser Arbeit war es YBa2Cu3O6+y Einkristalle bei höheren Drücken als zuvor mit NMR zu untersuchen. Dabei wurde der alte Rekord von 1.8GPa (Steven Reichardt 2018) auf 4.4GPa erhöht (aktuelle Arbeit). Da sich die Probenkammer in einer Druckzelle stark verformt, muss die Unversehrtheit der Kristalle an jedem Druckpunkt überprüft werden. Dies wurde unter anderem mit Bildern,welche mit dem Mikroskop durch die transparenten Anvils gemacht wurden, überprüft, als auch durch aufwendige Höhenmessungen der Probenkammer mit speziellen Mikroskopen in Verbindung mit einem Piezo-gesteuertem Probentisch. Durch die exakte Vermessung und Positionierung der Einkristalle auf dem Anvil konnte in Verbindung mit den Höhen- und Druchmessermessungen sichergestellt werden, dass sich der Kristall unter hydrostatischen Druckbedingungen befindet und nicht linear entlang der Zellenachse komprimiert wird, was zu einem Brechen oder einer Veränderung der Orientierung hätte führen können. Eine allgemeine Erkenntnis konnte dabei gewonnen werden, über die Stabilität, insbesondere der Höhe der Probenkammer, welche zunimmt mit dem Durchmesser des Culets. Dies ist entgegen des allgemeinen Prinzipes der Miniaturisierung zum erreichen höherer Drücke, für die Planung der Zellenarchitektur für Einkristallmessungen in NMR-Anvilzellen aber wichtig. Weiterhin mussten auch andere wichtige Parameter für NMR Messungen erfüllt werden. Die Architektur der Mikrospule welche in der Probenkammer um den Kristall gelegt wurde, mussten um den Füllfaktor zu maximieren an die Dimensionen der Kristalls angepasst werden. Dazu wurde eine Methode entwickelt um elliptische Mikrospulen von Hand zu wickeln, darin wurden die flachen Kristalle aufrecht platziert. Damit konnte das Signal auf eine annehmbare Intensität gebracht werden um in endlicher Zeit Messungen realisieren zu können. Mit den Messungen an Yttrium-Barium-Kupferoxid Einkristallen unter Druck konnte gezeigt werden, dass mit steigendem Druck sowohl die zunehmende Dotierung der Kupferoxidebene die Position am Sauerstoffatom bevorzugt, als auch eine Ladungsumverteilung in der Kupferoxidebene induziert wird. Weiterhin wurden NMR-Messungen am Indium Kern des Thermoelektrika Silber-Indium-Tellurid unter Druck durchgeführt. 5 verschiedenen Druckzellen wurden gebaut und bei Drücken bis zu 10GPa wurde gemessen. Bis 2.5GPa konnten Spektren aufgezeichnet werden die einen Anstieg des elektrischen Feldgradienten nahelegten. Dieser anstiegt konnte mit Nutationsexperimenten bestätigt werden. Die Echo-Experimente bei 4GPa und 5GPa wiesen einen starken Signalverlust auf und legten eine Quadropolaufspaltung des Zentralübergangs zweiter Ordnung nahe. Über 5GPa wurde kein Signal mehr gefunden. Nach dem Ablassen des Drucks zurück zu Umgebungsbedingungen wurde wieder ein Signal bei der ursprünglichen Frequenz gemessen.:0 Introduction 1 Theoretical Basics, Page 5 1.1 Nuclear Magnetic Resonance (NMR), Page 6 1.2 NMR Setup, Page 14 1.3 Pressure as Parameter, Page 17 1.4 NMR under Pressure, Page 28 2 Samples, Page 31 2.1 Yttrium-Barium-Copper-Oxide, Page 32 2.2 Silver-Indium-Telluride, Page 42 3 Experimental, Page 45 3.1 Spectrometer and Magnet, Page 46 3.2 Evaluation of the Measured Signals,Page 46 3.3 Micro Electronics, Page 47 3.4 Summary of the Chapter, Page 53 4 Sample Chamber Monitoring for single crystal NMR in high pressure cells, Page 55 4.1 Necessity of Sample Chamber Monitoring, Page 56 4.2 Measurements, Page 57 4.3 error consideration, Page 64 4.4 Discussion, Page 65 5 Single Crystal NMR of YBa2Cu3O6+y up to 4.4 GPa, Page 67 5.1 Doping Level and the Critical Temperature, Page 68 5.2 Orientation of the Single Crystal, Page 73 5.3 Discussion, Page 81 6 Silver-Indium-Telluride NMR under pressure, Page 83 6.1 Introduction, Page 84 6.2 Sample, Page 85 6.3 Pressures Cells, Page 85 6.4 Measurments, Page 87 6.5 Discussion, Page 97 7 Summary and Outlook, Page 99 7.1 Summary, Page 100 7.2 Conclusion and Outlook, Page 103 Appendix A Appendix, Page 107 A.1 Spectra, Page 108 Y-6.85 Cell, Page 108 Y-6.5 Cell, Page 113 References 127 / In this work the CuO2-plane of the high temperature superconductor yttrium-bariumcopper-oxide (YBa2Cu3O6+y) is investigated by nuclear magnetic resonance (NMR) under pressures up to 4.4GPa. Two high pressure NMR cells were built and filled with differently doped single crystals. The changes of the charge distribution in the CuO2-plane depending on doping and depending on pressure were the focus of the investigations. The motivation of this work was to extend the NMR measurements of YBa2Cu3O6+y single crystals in NMR anvil cells with pressures not achieved before. The old record (from Steven Reichardt 2018) of YBa2Cu3O6+y single crystals up to 1.8GPa was increased to 4.4GPa with this work. Due to the large deformation of the sample chamber, the integrity of a single crystal has to be checked at every pressure point. This was done by pictures, shot through the transparent anvils as well as height measurements of the sample chamber with a special microscope combined with a piezo controlled table. The exact measurements of the position of the single crystals as well as the height and diameter measurements assured that the single crystal is still in hydrostatic conditions or if it is tilted or pressurized linearly. A general cognizance about the stability of the sample chamber was acquired, especially about the stability of the height, which increases with the diameter of the culet. This is contrary to the general principle of miniaturization to reach higher pressures, if single crystals are of interest. The aim here is to have a stable sample chamber for good measuring conditions for NMR under pressure. Further, other expectations for the parameters of a NMR experiment had to be fulfilled as well. The architecture of a microcoil, which is placed around the crystal in the chamber, had to match the flat crystal shape to increase the filling factor and with this the signal to noise ratio (SNR) of the probe. For this, a method to wind elliptical micro coils by hand under the microscope was developed. Thereby signal intensity could be increased to an acceptable value which allowed more rapid measurements. With the measurements on YBa2Cu3O6+y single crystals under pressure it was shown that increasing pressure increase the hole doping in the CuO2-plane. Furthermore a redistibution of the charges in the CuO2-plane occurs. In a second part of this thesis 115In NMR measurements on the thermoelectric AgInTe2 under pressure up to 10GPa in 5 different cells were preformed. Up to 2.5GPa spectra were recorded which could be explained by an increase of the quadrupole frequency. This increase was verified by a power dependent nutation spectroscopy experiment. The echo experiments of pressures between 3GPa and 5GPa showed a high signal loss and pointed to an increasing disorder and a second order affected central transition of a powder spectrum. No signal was found above 5GPa despite elaborate searches in particular for a possible metallic component. After the pressure release a signal was found again at ambient conditions frequency.:0 Introduction 1 Theoretical Basics, Page 5 1.1 Nuclear Magnetic Resonance (NMR), Page 6 1.2 NMR Setup, Page 14 1.3 Pressure as Parameter, Page 17 1.4 NMR under Pressure, Page 28 2 Samples, Page 31 2.1 Yttrium-Barium-Copper-Oxide, Page 32 2.2 Silver-Indium-Telluride, Page 42 3 Experimental, Page 45 3.1 Spectrometer and Magnet, Page 46 3.2 Evaluation of the Measured Signals,Page 46 3.3 Micro Electronics, Page 47 3.4 Summary of the Chapter, Page 53 4 Sample Chamber Monitoring for single crystal NMR in high pressure cells, Page 55 4.1 Necessity of Sample Chamber Monitoring, Page 56 4.2 Measurements, Page 57 4.3 error consideration, Page 64 4.4 Discussion, Page 65 5 Single Crystal NMR of YBa2Cu3O6+y up to 4.4 GPa, Page 67 5.1 Doping Level and the Critical Temperature, Page 68 5.2 Orientation of the Single Crystal, Page 73 5.3 Discussion, Page 81 6 Silver-Indium-Telluride NMR under pressure, Page 83 6.1 Introduction, Page 84 6.2 Sample, Page 85 6.3 Pressures Cells, Page 85 6.4 Measurments, Page 87 6.5 Discussion, Page 97 7 Summary and Outlook, Page 99 7.1 Summary, Page 100 7.2 Conclusion and Outlook, Page 103 Appendix A Appendix, Page 107 A.1 Spectra, Page 108 Y-6.85 Cell, Page 108 Y-6.5 Cell, Page 113 References 127

Measurements of higher harmonics of the ac voltage response in YBCO thin film strips under low amplitude and low frequency harmonic excitation, as a function of temperature, show a non linear response of the conductivity in the superconducting transition interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak near Tc and their amplitudes seem to be closely related to the T-derivative of the first harmonic. The peaks are linearly dependent on the current amplitude and do not depend on frequency. The observed data are partially interpreted in terms of ac current induced thermal modulation of the sample temperature added to strong thermally activated fluctuations in the transition region. The fit of the model to the data gives information of some sample properties such as zero temperature critical current, zero onset resistance and thermal boundary conductance.

This dissertation presents the first reported identification and analyses of the phase relations in the YBa2Cu3O7-x (YBCO)-SiO2 system at elevated temperatures. In this regard, a rigorous characterization study of the reaction phases within YBCO glass fibers, heat-treated YBCO+SiO2 pellets, rapid thermally annealed YBCO+SiO2 rods and rapid thermally annealed YBCO powder inside a fused silica tube is provided. These analyses are based on a vast set of generated novel results obtained using energy dispersive spectroscopy analyses on an environmental scanning electron microscope, X-Ray diffraction analyses, Raman spectroscopy, X-ray photoelectron spectroscopy analyses and a cross-polarized light study. First, original drawings of YBCO into glass fibers using the molten-core approach on a fiber draw tower in air and oxygen atmospheres are presented and analyzed. The performed analyses reveal the occurrence of reactions between the YBCO core and the silica cladding in as-drawn fibers as well as after additional heat-treatments. A detailed analysis and characterization of the occurring dissolution and diffusion based reaction processes is, then, provided along with the identification of the arising phase separation. Moreover, in order to analyze drawing YBCO glass fibers at lower temperatures, the use of borosilicate as the preform material is also investigated. This varied set of experiments and associated analyses reveal that the as-drawn YBCO fibers contain an amorphous core and that cuprite (Cu2O) is the first phase to crystallize out of the amorphous silicate matrix upon heat-treatment. Furthermore, the obtained results demonstrate the dissolution of the fused silica cladding into Si4+ and O2- ions and their subsequent diffusion into the molten YBCO core, leading to phase separation due to an occurring miscibility gap in the YBCO-SiO2 system as well as to silicate formation and amorphization of the YBCO core. This, as a result, prohibits the formation of the superconductive YBCO (Y-123) phase upon annealing. In addition, heat-treatment analyses show that higher temperatures or prolonged dwelling times at lower temperatures lead to the formation of barium copper and yttrium barium silicates. The analysis focusing on the use of borosilicate as the preform material reveals that drawing at lower temperatures reduces the dissolution and diffusion based reactions, but does not prevent them. Furthermore, the analysis on YBCO glass fibers with a fused silica cladding drawn in oxygen atmosphere shows that a higher oxygen content increases the dissolution of the fused silica cladding into its ions and their subsequent diffusion into the molten YBCO core. In addition, the performed heat-treatments on YBCO+SiO2 pellets in air and oxygen atmospheres demonstrate the gradual decomposition of the Y-123 phase with an increase in SiO2 content. Moreover, the rapid thermal annealing experiments with a subsequent quenching step on YBCO+SiO2 rods and on YBCO powder inserted inside a fused silica tube show the decomposition of the Y-123 phase and the formation of phases similar to the phases obtained in the YBCO glass fiber study, thus corroborating the results thereof. In summary, this dissertation enables the determination of the phase relations and reaction processes within the YBCO-SiO2 system, the identification of the direct effects of the silicon content on the Y-123 phase decomposition, as well as a rigorous characterization of the dissolution and diffusion based reactions within the YBCO-SiO2 glass-clad fiber system. The generated results and drawn conclusions build a fundamental understanding of phase relations in the YBCO-SiO2 system, which enables a definite assessment of the feasibility of manufacturing long-scale purely superconductive YBCO glass fibers using the molten-core approach and introduces advanced contributions to general glass-clad fiber systems manufactured using this method. / Doctor of Philosophy / This dissertation provides the first reported identification and analysis of the phase relations in the YBa2Cu3O7-x (YBCO)-SiO2 system at high temperatures. In this regard, a thorough characterization study of the reaction phases within YBCO glass fibers drawn using the molten-core approach on a fiber draw tower is provided. In addition, heat-treatment analyses considering YBCO+SiO2 pellets, rapid thermally annealed YBCO+SiO2 rods and rapid thermally annealed YBCO powder inside a fused silica tube are performed to gain further fundamental insights. The performed analyses are based on a wide set of characterization methods including energy dispersive spectroscopy on an environmental scanning electron microscope, X-Ray diffraction analyses, Raman spectroscopy, X-ray photoelectron spectroscopy and a cross-polarized light study. Our experimental results and performed analyses identify the phase relations and reaction processes within the YBCO-SiO2 system at elevated temperatures, demonstrate the direct effects of the silicon content on the superconductive YBCO phase decomposition, enable drawing definite conclusions regarding the feasibility of manufacturing long-scale purely superconductive YBCO glass fibers using the molten-core approach, and, characterize the dissolution and diffusion based reactions occurring within the YBCO-SiO2 glass-clad fiber system. In a nutshell, this dissertation provides a fundamental understanding of phase relations in the YBCO-SiO2 glass-clad system as well as key insights covering general glass-clad fibers drawn using the molten-core approach, paving the way for improved glass-clad fiber manufacturing using this method.

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.