New Fabrication Process of High-Tc Oxide Superconductors via Melt and Their Characterization

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Preparation techniques for high-Tc oxide superconductors via melt have attracted much interest because dense and homogeneous materials are easily obtained. The purpose of this research project is to establish the preparation processes via melt to obtain excellent high-Tc superconductors with various morphologies. The following results were obtained.1. Viscosities were measured for the Bi-Ca-Sr-Cu-O glasses with various compositions in order to predict the compositions for fiber drawing. The Bi-Pb-Ca-Sr-Cu-O glass fibers were successfully prepared using a thermal-image furnace.2. The crystallization process was studied for the Bi-based superconductor precursor glasses ; the phases of Ca_2PbO_4 and CuO formed during heat treatment, which enhanced the partial melting of the samples, was found to play an important role in the formation of the 110 K phase.3. The optimum heat-treatment temperatures T_<OPT> was observed in the metal-doped superconductor glass-ceramics in the systems Bi-Pb-M-C … More a-Sr-Cu-O(M : various metals). The metal dopants were found to affect the temperature at which a partial melting occurred and therefore affect T_<OPT>.4. The introduction of the multi-step heat-treatment process, by which the nucleation was expected to be accelerated, was found to enhance the critical current density of Bi-Pb-Ca-Sr-Cu-O glass-ceramics obtained from rapidly quenched precursor glasses.5. Preparation condition of high-Tc thick films by melt solidification was optimized. Rapid cooling of the molten samples to the heat treatment temperature was the most important factor in all the preparation steps.6. Metal doped superconductor thick films of Bi-Pb-M-Ca-Sr-Cu-O(M=In, Mo, Nb, Sb, Sn, V, W) were prepared using melt-solidification procedure. The dopants lowered the partial melting temperatures and thus lowered T_<OPT> for the formation of the 110 K phase.7. Fine powders in the system Bi-Pb-Ca-Sr-Cu-O were successfully prepared by the spray-pyrolysis method. The particles produced were spherical and their size could be controlled from submicrometer to micrometer by changing the concentration of the starting solutions. Less