Date of Award
Doctor of Philosophy
James R. Thompson
Tolga Aytug, Adriana Moreo, Hanno H. Weitering, Veerle Keppens
Significant progress has been made in the development of YBa2Cu3O7-x (YBCO)-based coated conductors (CCs) since the discovery of YBCO in 1987. Nowadays, high temperature superconductor (HTS) materials are advancing toward wide application areas in medical physics, industry, and science. The successful applications of these materials require clear understanding of the mechanisms controlling the current carrying capacity. It has been demonstrated the maximum current that a HTS can support is strongly affected by the vortex dynamics within the HTS materials. In this dissertation, we employed a combination of methods: conventional transport, magnetometry in a swept magnetic field, and “flux creep” measurements to obtain current density J vs. electric field E characteristics. Moreover, we determined the superconducting properties of the HTS materials as a function of temperature, magnetic field strength, and field orientation. Another significant issue in the commercialization of HTS materials is the manufacturing cost of CCs. Although the superconducting films can be deposited on the flexible biaxially textured coating on metallic substrates with high quality performance, these substrates require deposition of several buffer layers to achieve high quality HTS coatings. Hence, in the second part of this thesis, we focused on the simplification of the Ion Beam Assisted Deposition (IBAD) buffer architecture. Development of a simplified architecture is one of the key issues for reduced manufacturing cost of second generation superconducting wire production. In this thesis, we demonstrated that the present IBAD template can be simplified by eliminating one of the buffer layers from the standard architecture. In addition, we displayed that the LaMnO3 (LMO) cap layers can be further functionalized by replacing it a nanocomposite LMO:MgO cap layer, resulting in two-phase separated composite MgO nanostructures within the LMO matrix. Measurements of orientation-dependent Jc of YBCO coatings deposited on these nanostructured cap buffer layers revealed enhanced correlated c-axis pinning and improved in-field Jc performance. Our results underscore that (i) better understanding of vortex dynamics is a very valuable tool to establish practical level of HTS operation and (ii) formulation of novel material fabrication approaches is indispensable in the pursuit of more efficient, economical, high performance superconducting devices.
Polat, Özgür, "Wide-Range Characterization of Current Conduction in Superconductors-Tuning Their Properties by Nanoscale Modification of Materials. " PhD diss., University of Tennessee, 2009.