PREPARATION OF GRAIN-ALIGNED BULK (2223)B(PB)SCCO SUPERCONDUCTOR WITHIMPROVED J(C) BY HOT-TEXTURING

Bulk Bi1.84Pb0.34Sr1.81Ca2.03Cu3.06Ox superconductors with relative de nsity in the range 88-90% were prepared by high cold pressing + pressu reless sintering and subsequently hot forged to increase the extent of grain orientation. It has been found that the final density of the sa mples exceeds 95% and the orientation factor increases up to approxima te to 80%. The introduction of a short high-temperature treatment (T = 885 degrees C) promotes the extrusion of secondary phases, leaving in the sample only the (2223) as a superconducting phase and islands of Ca-Sr-Cu-O and CuO. The annealing at 400 degrees C in oxygen was found essential to recover the oxygen content, lost during densification an d texturing treatments, and to increase the T-c0 value up to 100-105 K . The employment of pressureless sintered samples (PLS) together with the step at 885 degrees C implies the release of the disorder near sub -grain boundaries usually found in hot-pressed samples. As a consequen ce of these features, textured PLS samples show a J(c) value at 77 K o ne order of magnitude higher with respect to the simple PLS sample. Th e use of sol-gel powder improves the densification and texturing of th e superconductor even for shorter treatment times. Since J(c) of this sample is congruent to 700 A/cm(2), the addition to the treatment of t he step at 885 degrees C is highly promising in the view to reach a fu rther increase of critical current density.