Fabrication of stable superconductive wires with YBa₂Cu ₃O_x/Ag₂O composite core

The problem of maintaining the oxygen stoichiometry of the Y ₁Ba₂Cu₃O_x (the so-called 123) compound at the desired level of x=6.0±0.1 when fabricating superconducting wires using the powder-in-tube method is addressed. A solution to this problem appears to be incorporating an unstable oxide like Ag ₂O in the core material, such that it acts as an in situ oxygen donor during the final sintering or annealing stage. Moreover, the segregation of Ag at the grain boundaries of the 123 grains and at the porosities seems to be a possible reason for the considerable improvement of the critical current density J_c of these wires. The effect of processing parameters, like different sintering temperatures and addition of various percentages of either Ag or Ag₂O, is presented. Finally, in order to test conservation of superconductive properties during handling, the wires were subjected to different degrees of bending, and the subsequent effect on superconducting transition temperature, T_c and J_c, is reported.