Bi(2223)/Ag monofilamentary tapes have been characterized by measurements of j, vs. B and vs. 8, the angle between the applied magnetic field and the c axis. High degree of texturing, high density and Bi(2223) single phase conditions were found to be the major effects leading to high jc values. A further condition for reaching the highest jc values is a very low overall carbon content, the presence of carbon at the grain boundaries acting as a strong limiting factor. The highest value of jc in the present work is 4.104 A/cm2 at 77K,OT, corresponding to more than 2.105 A/cm2 at 4.2K,OT.

No abstract

A large increase (∼8×) in critical current density, Jc, was achieved for in situ laser ablated YBa2Cu3O7−δ–Ag films. High-resolution Auger electron spectroscopic investigation indicates that the Ag-doped films are stoichiometric with a relatively low grain-boundary extension (8 nm) in contrast to undoped YBa2Cu3O7−δ films (32 nm). Further analysis suggests that the doped film contains a much lower silver content (<0.15 wt %) than in the target material (5 wt %). These observations are in excellent agreement with the temperature dependence of Jc, the room-temperature resistivity, and the surface resistance results. Thus, Jc enhancement in Ag-doped films can be attributed to their superior properties, viz., improved microstructure characteristics and the reduced resistive grain boundaries.

Abstrad-An extensive study of the detrimental effect of C on critical current densities (ic) of Ag sheathed Bi(2223) tapes has been carried out. High j, can only be obtained if the C content is kept to a minimum. Successive calcination steps at 820°C are effective in reducing the amount of C in the resulting powders. On the other hand, high energy milling increases the amount of C in the powder. Controlled quantities of C impurities were introduced into the powders by performing the calcinations in a CO, rich atmosphere. The j, measured on tapes obtained with C rich precursors are lower by a factor of 2 to 4 than the j, of tapes from powders calcined in air.

No abstract