Fabricates yttrium barium copper oxide (YBCO) thin films embedded with cerium oxide (CeO2) nanoparticles using pulsed laser deposition (PLD). Studies the effects of CeO2nanodots in the YBCO matrix. Examines varies methods of improving critical current density (J[subscript]c) of high temperature superconductors by flux-pinning, specifically in YBCO.
Since the discovery of the high temperature superconductor YBa2Cu3O7-[delta] (YBCO), with transition temperature (Tc = 77 K), above liquid nitrogen point in 1987 many research projects have been dedicated to enhancing the high field performance of this material for practical applications. The 2nd generation YBCO-based coated conductors are believed to be the most promising approach for commercial applications including power transmission, motors, generators, and high field magnets. With the advances of nanotechnologies, different nanoengineering methods have been demonstrated to enhance the performance of YBCO thin films, include doping with 0-dimensional (0-D) self-assembled nanoparticles, 1-dimensional (1-D) nanorods, and 2-dimensional (2-D) nanolayers. Furthermore, dopants with ferromagnetic properties are also reported to provide enhanced pinning effects by Lorentz force, especially under high-applied magnetic fields. The principle of these methods is to generate high-density defects at the heterogeneous interfaces as artificial pinning centers in an effort to improve the flux-pinning properties. The morphology and dimensions of the nanoinclusions play an important role in pining enhancement. Optimized pinning structures are likely to be located at energetically favorable vortex cores, which form a triangular lattice with dimensions close to the YBCO coherence length [xi]([xi]ab ~ 4 nm; [xi]c ~ 0.5 nm at 77 K.) However, it is challenging to achieve small dimensional nanodopants in the vapor deposited YBCO thin films. The purpose of this research is to utilize nanoengineering methods to produce optimized pinning structure in YBCO thin films. In this thesis, we systematically study the effects of different nanoinclusions on the flux-pinning properties of YBCO thin films. The 0-D ferromagnetic Fe2O3 and CoFe2O4 nanoparticles, 2-D CeO2 multilayers, and tunable vertically aligned nanocomposites (VAN) of (Fe2O3)x:(CeO2)1-x and (CoFe2O4)x:(CeO2)1-x systems are introduced into the YBCO matrix as artificial pinning centers. Results suggest that all nanoinclusions showed significant enhancement in the superconducting properties of YBCO. The ferromagnetic pinning centers dominate at high field and low temperature regimes, however, the defect pinning centers dominate at low field and high temperature regimes. The uniquely arranged VAN structure of alternating magnetic and non-magnetic nanophases, which incorporates both high defect density and tunable distribution of magnetic dopants, is believed to be an ideal solution for flux-pinning enhancement. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149478
High-{Tc} superconducting thin films of YBa2Cu3O{sub 7 -{delta}} (YBCO) were deposited on sapphire substrates with buffer layers of yttria-stabilized zirconia and cerium oxide by using pulsed laser deposition (PLD) technique. The epitaxial relationship between the substrate and buffer layers as well as the buffer layer and the superconducting film was established. Furthermore, using the same thin film technique, YBCO superconducting thin films were deposited on both sides of substrates of up to 5 cm in diameter. The superconducting properties of the films on both the sapphire with buffer layers and large-area substrates were comparable to the ones of the best YBCO films. 8 refs., 6 figs.
