Composite metallic sheathes: the key to low-cost, high strength (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀-based tapes?

(Bi, Pb)(2)Sr2Ca2Cu3O10-based superconducting tapes were prepared by the powder- in- tube process, using a bimetallic sheath consisting of Ag and Ni. Ag was in contact with the superconducting ceramic core and acted as a protective layer against reaction between the external Ni sheath and the core. (Bi, Pb)(2)Sr2Ca2Cu3O10 phase formation was possible if a path for oxygen diffusion was opened in the Ni sheath.

This was achieved by removing Ni on one edge of the tape edges by polishing. Transport critical current densities as high as 35 000 A cm(-2) (77 K, self- field), corresponding to a j(e) of about 11 000 A cm(-2), were achieved in a single heat-treatment. The efficient protection offered by the Ag layer against Ni diffusion into the ceramic core suggests that Ag layers as thin as 5 mu m may be applied, thus reducing the production costs.

The superior stiffness of Ni provides a stronger sheath, greatly improving the mechanical stability of the composite, and may be responsible for the high ceramic densities and critical current densities obtained without intermediate densification.