Microstructure-properties relationships in yttrium- and bismuth-based high critical transition temperature superconductors
Chen, Jiangang
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Permalink
https://hdl.handle.net/2142/21914
Description
Title
Microstructure-properties relationships in yttrium- and bismuth-based high critical transition temperature superconductors
Author(s)
Chen, Jiangang
Issue Date
1991
Doctoral Committee Chair(s)
Wayman, C. Marvin
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
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.
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