Processing and microstructural characterization of a lithium doped and undoped polycrystalline bismuth(2) strontium(2) calcium copper(2) oxygen(x)
Wu, Shiming
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https://hdl.handle.net/2142/21222
Description
Title
Processing and microstructural characterization of a lithium doped and undoped polycrystalline bismuth(2) strontium(2) calcium copper(2) oxygen(x)
Author(s)
Wu, Shiming
Issue Date
1994
Doctoral Committee Chair(s)
Schwartz, Justin
Department of Study
Nuclear, Plasma, and Radiological Engineering
Discipline
Nuclear Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Engineering, Materials Science
Language
eng
Abstract
The high T$\sb{\rm c}$ superconducting oxide Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ (Bi2212) is very promising for the magnet and device applications.
Amorphous Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ powder was partial-melt sintered to obtain the high T$\sb{\rm c}$ superconducting Bi2212 phase. Resulting samples are multi-phased due to incongruent melting and the significant Bi loss during sintering. In order to reach a high volume fraction of Bi2212 phase, adjustments were made on the stoichiometry of precursor powders and processing conditions. Compared to the nominal Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ starting stoichiometry and ambient air sintering, starting powders with excess Bi content and/or a Bi-rich atmosphere during sintering resulted in reduced secondary phase volume fraction and enhanced 2212 phase volume fraction.
Superconducting properties and microstructural evolution of Li doped Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ were studied. For the optimum doping, $\rm T\sb{c,onset} > 100\ K$ was observed and T$\sb{\rm c,zero}$ increased 10 K from undoped Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ to 94.1 K. Li doped Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ systems exhibit similar phase formation sequence from the melt as undoped but at significantly lower temperatures. The liquid phase formed at lower temperatures in Li-doped powders promoted the formation of the 2212 phase. The Cu-free phase was found in the Li-substituted for Cu samples, while a Cu-O phase was found in the Li added to Bi$\sb2$Sr$\sb2$CaCu$\sb2$O$\sb{\rm x}$ samples. The Cu content of the 2212 grains in the Li doped samples was lower than that in the undoped ones. Therefore, Li partially occupied the Cu sites and possibly resided at interstices in the 2212 phase.
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