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 Title: Microstructure-properties relationships in yttrium- and bismuth-based high critical transition temperature superconductors Author(s): Chen, Jiangang Doctoral Committee Chair(s): Wayman, C. Marvin Department / Program: Materials Science and Engineering Discipline: Materials Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Physics, Condensed Matter Engineering, Metallurgy Engineering, Materials Science Abstract: The thermodynamic and kinetic behavior of superconducting phases during the crystallization annealing process have been observed and analyzed in crystallized Bi-Sr-Ca-Cu-O glass samples. The microstructural characteristics of the 85 K and 110 K phases, and impurities and defects in crystallized samples were studied using transmission electron microscopy. The density of precipitates and lattice defects is greatly increased as the calcium and copper content of the starting materials increase.The magnetization critical current density J$\sb{\rm c}$ has been found to increase about 100 times in magnitude as the density of impurities and lattice defects is increased. Analysis indicates that the Ca- and Cu-rich precipitates could act as normal and volume pins via magnetic interaction.The superconducting transition temperature T$\sb{\rm c}$ has been found to vary in YBa$\sb2$Cu$\sb3$O$\sb{\rm x}$ samples with different oxygen stoichiometry. The magnetization J$\sb{\rm c}$ are strongly affected by the variation of the superconducting properties and the microstructure. Twin boundaries could serve as a type of pinning center with normal and surface pins via core interaction.The microstructures of polycrystalline YBa$\sb2$Cu$\sb3$O$\sb{\rm x}$ were varied through different sintering conditions to study transport-current characteristics in a magnetic field. Transport critical current density J$\sb{\rm c}$ (H) is severely suppressed as the grain boundaries are contaminated with second phases. The critical-current behavior and closely related microstructural changes are explained by a Josephson weak-link model.YBa$\sb2$Cu$\sb3$O$\sb{\rm x}$ compounds fabricated by a zone melting process showed a significantly enhanced magnetization J$\sb{\rm c}$ and transport J$\sb{\rm c}$ in magnetic field. Dominant low-angle grain boundaries, a high density of dislocations and dispersed fine Y$\sb2$BaCuO$\sb5$ particles have been found in the samples. The microstructural characteristics of these defects were studied using analytical TEM. The origin of the defects and impurities as well as their roles acting as effective flux pinning centers are also discussed. Issue Date: 1991 Type: Text Language: English URI: http://hdl.handle.net/2142/21914 Rights Information: Copyright 1991 Chen, Jiangang Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9210763 OCLC Identifier: (UMI)AAI9210763
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