PROPERTIES OF ALLOY PRECURSORS AND THE RESULTING SUPERCONDUCTING YBA2CU3O7-DELTA-AG COMPOSITES

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-degrees-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 T(c) of 90 K. Superconductivity is achieved only when the alloy is oxidized above the solidus temperature, where the presence of liquid phase enables the oxides to be concentrated and connected.