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Synthesis, processing behavior, and characterization of bismuth superconductors using freeze dried nitrate precursors

Published online by Cambridge University Press:  03 March 2011

N.V. Coppa
Affiliation:
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
W.L. Hults
Affiliation:
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
J.L. Smith
Affiliation:
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
J. Brynestad
Affiliation:
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6100
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Abstract

The synthesis of Bi2−xPbxSr2Ca2Cu3O10 (Bi2223) powders from a freeze dried nitrate precursor is reported here. We examine the composition and morphology of the precursor material, describe the chemistry and kinetics of product formation, and evaluate the phase composition and superconducting properties of the products. A nitrate solution containing the appropriate ratio of cations was rapidly frozen and then freeze dried at low temperatures to form an atomic mixture of the component salts. The thermal processing of the freeze dried material consisted of three steps: (i) dehydration, (ii) denitration, and (iii) solid state reaction to form the Bi2223 superconducting product. Calcium-substituted bismuthates and strontium-substituted calcium cuprate, not Bi2201, are the intermediates between the nitrates and the superconducting products. These highly disordered phases rapidly transform into Bi2212 or Bi2223 at higher temperatures (≍790 °C). The kinetics of product formation was studied using XRD analysis and magnetic susceptibility. The kinetics were shown to follow the nucleation and growth mechanism. Bi2223 formed after only 30 min at a few degrees below the melting point, and after 37 h Bi2223 products exhibited excellent phase composition and magnetic susceptibility characteristics.

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Articles
Copyright
Copyright © Materials Research Society 1994

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References

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