New Technology to improve texturing and transport current in bulk (2223) BSCCO superconductors

Bulk BSCCO (2223) was prepared by a multi-step process (high cold pressing + pressureless sintering + hot-forging (HF)) to increase the extent of grain orientation. It has been found that the final density of the samples exceeds 95% and the orientation factor increases up to ≈80%. Powders were prepared with different techniques starting by several nominal compositions. The introduction of a short high-temperature treatment during HF, acts as a purifying process, promoting in addition the extrusion of secondary phases and leaving in the sample only the (2223) as a superconducting phase and islands of Ca-Sr-Cu-O and CuO. In the case of the powder nearest to the stoichiometric composition, an annealing at 400°C in oxygen was found essential to recover the oxygen content, lost during densification and texturing treatments, and to increase T_c0. Samples prepared with powder having calcium and copper excess do not contain (2212) phase even after hot-forging. As a consequence, J_ct value of the textured samples, at 77K, reaches ≈10000A/cm², i.e. two order of magnitude higher in respect to the simple PLS sample. The use of sol-gel powder improves the texturing of the final samples, while J_c values result less improved than expected, due to the huge growth of secondary phases precipitates.