Properties of alloy precursors and the resulting superconducting YBa2Cu3O7−δ-Ag composites

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Abstract
A significant obstacle to the widespread application of high‐temperature superconductors are the poor mechanical properties of these oxides. A novel processing technique was investigated that attempts to circumvent this problem using ductile alloy precursors to superconducting composites. Alloys of composition Y‐2Ba‐3Cu‐Ag were prepared by arc‐ and induction melting the metals. A variety of mechanical tests show that alloys with 90 wt % Ag are ductile, and differential thermal analysis indicates a solidus temperature of 703 °C. Using thermogravimetric analysis, the oxidation rate of Y‐2Ba‐3Cu‐90 wt % Ag alloys was studied. This rate does not follow that which is expected based upon the theory of internal oxidation, nor is there a transition to external oxidation upon lowering the partial pressure of oxygen. The superconducting properties of the oxide in the resulting composite are similar to those of polycrystalline samples, with a Tc of 90 K. Superconductivity is achieved only when the alloy is oxidized above the solidus temperature, where the presence of a liquid phase enables the oxides to be concentrated and connected.