A multi-step process to improve texturing and transport current in BSCCO (2223) superconductors
Bulk BSCCO(2223) was prepared by a multi-step process (high cold pressing+pressureless sintering+hot-forging): the final density of the samples exceeds 95% and the orientation factor increases up to /spl ap/86%. It was found that the process phenomenology is strictly linked to the starting powder stoichiometry and characteristics: when composition is very near to the theoretical (2223), effects of secondary phase extrusion are observed during hot-forging, yielding a purification and inhibition of (2212) formation, accompanied by an appreciable increase of J/sub c/ with respect to hot-pressed samples. When the Ca/Sr ratio is considerably >1, recrystallisation of (2223) from the liquid takes place, with a remarkable improvement of critical current density (J/sub c/>10/sup 4/ A/cm/sup 2/). In this case, the non-superconducting secondary phases act as an intrinsic oxygen reservoir. Finally, when composition diverges even more from (2223) (Ca/Sr/spl Gt/1 and Cu excess), the formation of too many precipitates of non-superconducting phases hinders the texturing process and more in general deteriorates the intergranular properties.