Preparation of Bi-Pb-Sr-Ca-Cu-O Superconductor By Thermal Decomposition of an Edta Colloid
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PREPARATION OF Bi-Pb-Sr-Ca-Cu-O SUPERCONDUCTOR BY THERMAL DECOMPOSITION OF AN EDTA COLLOID
H.S.Koo*, C.K.Chiang*, Y.T.Huang* and G.C.Tu** * Materials Research Laboratories, Industrial Technology Research Institute, Hsinchu, 31015, Taiwan, R.O.C. ** Institute of Materials Science and Engineering, National Chiao-Tung University, Hsinchu, 30049, Taiwan, R.O.C.
ABSTRACT High-Tc superconducting Bi-Pb-Sr-Ca-Cu oxide with zero resistance temperature at above lOOK has been synthesized via the use of ethylenediamine-tetra-acetate(EDTA) colloid and corresponding metal nitrates. Remarkable sinterability of the precursor requires shorter time to achieve superconducting phases than conventional solid-state reactions. Superconducting properties were measured electrically and magnetically. The thermal decomposition, X-ray diffraction and microstructural characteristics of the precursor and the sintered samples were also discussed.
INTRODUCTION Since the reports on the occurrence of the superconductivity at about 30K in the Ba-La-Cu-O[l] and 90K in the Y-Ba-Cu-0[2] systems, researchers are encouraged to investigate mechanism, higher-Tc superconductors and appropriate processing techniques for application interests. More recently, superconductivity at above 100K in the new Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O systems were discovered by Maeda et al.[3] and Sheng et al.[4], respectively. Although the highest-Tc superconductor is found in the Tl-based Tl 2 Ba 2 Ca 2 Cu 3OY(5], the Bi-based superconductors are still regarded as the most potential materials because of the stable moisture resistance and its nontoxic character. At present, most superconducting oxides are prepared by solid state reaction through the mechanical/manual mixing of oxides and carbonates. Compare to chemical synthesis routes, this traditional way is difficult to achieve a precise control for powder characterizations such as homogeneity, particle size, particle distribution and morphology. The characteristics of the synthesized powder will impact the physical/mechanical properties of the final sintered products. The object of this search is to develope a chemical synthesis route for the preparation of Bi-Pb-Sr-Ca-Cu-O superconductors through the thermal decomposition of an EDTA colloid, in an attempt to have a better control over the final products.
EXPERIMENTAL The initial step in our process was the preparation of a nitratesethylene glycol solution with stoichiometric metal molar ratio (Bi:Pb:Sr:Ca:Cu) - 1.68:0.32:1.75:1.85:2.80. Reagent-grade metal nitrates were individually dissolved in ethylene glycol and stirred to obtain a transparent light blue solution. Separately, ethylene-diamine-tetra-acetic acid was added to another ethylene glycol and the pH was adjusted to above 7.0 with ammonium hydroxide to dissolve the EDTA powder. The metal nitrates-EDTA solution was prepared by mixing the nitratesethylene glycol solution and EDTA-ethylene glycol solution, which yielded a mixture in deep blue. The resulting solution was heated to vaporize the Mat. Res. Soc. Symp
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