Bi-2223 bulk superconductor with oriented texture and high transport critical current

BSCCO (2223) superconducting powders were prepared by three different techniques (solid state, pyrolysis and sol-gel) and with three different stoichiometries, essentially based on variations of the Ca/Sr ratio and the Cu concentration. Pressureless sintering was performed on cold uniaxially pressed (1 GPa) samples, avoiding the drawbacks connected with hot pressing; different hot-forging cycles were then applied to attain a greater density and orientation factor. It was found that the process phenomenology is strictly linked to the powder starting stoichiometry: when the composition is very near to the theoretical (2223), the effects of the secondary phase extrusion are observed during hot forging, yielding a purification and inhibition of (2212) formation accompanied by an appreciable increase of J_c with respect to the hot-pressed samples. On the other hand, when the Ca/Sr ratio is considerably greater than one and the Cu excess is low, recrystallization of (2223) from the liquid takes place, with a remarkable improvement of the critical current density (J_c>10⁴ A cm^-2).