Crystalline orientation engineering and charge transport in thin film YBa(2)Cu(3)O(7-x) superconducting surface-coated conductors

The weak-link behavior of grain boundaries in polycrystalline high-T _c superconductors adversely affects the current density in these materials. The development of wire technology based on polycrystalline high-T_c materials requires understanding and controlling the development of low-angle grain boundaries in these conductors. The research goal is to comprehensively examine the methodology in fabrication and characterization to understand the structure-transport correlation in YBa₂Cu₃O _7−x (YBCO) surface-coated conductors.; High current density YBCO coated conductors were fabricated and characterized as candidates for second generation high-T_c wire technology. Critical current densities (J_c) greater than 1 × 106 A/cm2 at 77 K and zero magnetic field were obtained using thin films epitaxially grown by metalorganic chemical vapor deposition (MOCVD) and pulsed laser deposition (PLD) on oriented buffer layers. The biaxially textured oxide buffer layers were deposited by ion-beam-assisted deposition (IBAD). The transport properties of coated conductors were evaluated in high magnetic fields for intrinsic and extrinsic flux vortex pinning effects for improved high-field properties. Transport J_c's of these coated conductors at 7 tesla (77 K) were measured at values greater than 105 A/cm 2 with the magnetic field perpendicular to the YBCO c-axis (B⊥ c) in both MOCVD and PLD derived conductors. The J_c's in B || c orientation fell an order of magnitude lower at 7 tesla to values near 10 4 A/cm2 due to decreased intrinsic flux pinning. The critical current densities as a function of grain boundary misorientation were found to deviate from the general trend determined for single grain boundary junctions, due to the mosaic structure, which allows meandering current flow.; Extensive parametric investigations of relevant thin film growth techniques were utilized to establish growth-property relationships that led to optimized fabrication of high-T_c conductors. The work contained in this dissertation successfully addresses the challenge in engineering low-angle grain boundary polycrystalline conductors for high-current high-field applications and develops a structure-property correlation, which is essential for advancing this technology.