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Title Investigation of mixed rare earth (RE123) cuprate superconducting thin films grown by laser ablation and Sol-Gel techniques
Author Wulff, Anders Christian (Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract The Pulsed Laser Deposition (PLD) technique was used to fabricate a series of single and mixed RE123 (Nd, Sm and Gd) superconducting thin ¯lms. Precursor metal oxide powders was prepared and a target for PLD was fabricated. A mixed triple RE123 system with 33 % of each of the (Nd, Sm and Gd) rare earth cations was fabricated alongside with the single Gd123 system. The ¯lms were characterized by means of X-ray di®raction analysis, surface morphology by means of SEM, AFM and optical microscopy. The superconducting properties of the ¯lms were investi- gated using ac susceptibility and magnetic hysteresis loop measurements. The NSG123 thin ¯lms showed no superconducting transition above 16 K. The resulting critical temperature value for the Gd123 thin ¯lms was in the high temperature superconductor (HTS) range and comparable to that found by others. The crystal quality was found to increase with decreasing growth rate and various growth modes have been proposed as possible origins for the resulting ¯lms. The FWHM of the c-axis peaks was in general higher for the NSG123 ¯lms compared to the Gd123. A higher partial oxygen pressure during deposition was found to increase the surface roughness. Furthermore, it was found that a mixture of argon and oxygen acts as an e®ective total pressure of oxygen, if the oxygen pressure is su±cient. An oxygen content model was applied to the ¯lms and the level were found to be in good agreement, with some modi¯cations, with that found by others. An optimal range was found for the oxygen content and the HTS ¯lms were found to be within or above this range indicating an orthorhombic structure. Magnetic hysteresis loop measurements for two of the Gd123 ¯lms were converted into critical current curves by means of an extended Bean Model for thin ¯lms. The critical current densities for the best performing Gd123 ¯lm was a factor of 50 or more lower, compared to that found by others. A region of "good" (c-axis) deposition parameters regarding partial oxygen pressure and substrate temperature has been found. A scaling analysis method was applied to the critical current density for the Gd123 ¯lms in order to investigate the pinning mechanisms of the ¯lms. A number of possible pinning mechanisms have been suggested based on theoretical ¯ts. A series of water based gels were fabricated using the Sol-Gel technique. Precursor acetate powders were used in combination with a Tri-Ethanol-Amine (TEA), a complexing agent. A 0.6 M NSG123 gel, a 0.6 M Gd123 gel and a 0.12 M Gd123 gel were prepared. A number of ¯lms were fabricated by drop-coating, using the 0.6 M gels, on silver, Ag, substrates. The phase was investigated using high energy X-ray di®raction. The NSG123 and Gd123 gel prepared ¯lms showed similar phases. Future requirements for an in-situ investigation, of relatively thick gel based ¯lms, during sintering was found. The ¯lm needs to be tilted by some angle.
Imprint Danmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi : Roskilde
Pages 121
Keywords Materialeforskning; Materials research; Superledende materialer til energisektoren; Superconducting materials for the energy sector
Fulltext
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Admin Creation date: 2009-07-29    Update date: 2010-12-01    Source: dtu    ID: 247405    Original MXD