PREPARATION BY IN-SITU REACTION AND PHYSICAL CHARACTERIZATION OF AG(AU) AND AG( PD) SHEATHED(TL, PB, BI)(SR, BA)(2)CA2CU3O9-DELTA TAPES

Superconducting tapes with high-purity substituted Tl(1223) powders (> 95 wt.%, T-c similar to 120 K) were produced by a new method based on an in-situ reaction under high pressure of helium (25 bar He/0.5 bar O-2). A Ag(20 wt.% Au) alloy showed to be a good sheath material for an in-tape reaction up to 990 degrees C, even when involving partial melting of the oxide which favors the grain growth. Due to an interaction between Pd and the oxide, a Ag(6 wt.% Pd) alloy is much less suitable for tape preparation, Reproducible transport critical current densities of 9 kA/cm(2) (77 K, 0 T) were obtained for Ag(Au) sheathed Tl(1223) tapes with in-tape-reacted powder, the highest value being 10 kA/cm(2). The magnetic-field dependence of j(c) of such tapes was improved with respect to Ag sheathed tapes with pre-reacted Tl(1223) powders. Locally textured samples with up to 50 mu m large plate-like grains were obtained after partial melting in Ag(Au) sheathed tapes.