A multi-step process to improve texturing and transport current in BSCCO (2223) superconductors

Abstract

Abslruct-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 *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, respect to hotpressed samples. When Ca/Sr ratio is considerably >1, recrystallisation of (2223) from the liquid takes place, with a remarkable improvement of critical current density (Jc > lo4 A/cm2). In this case, the non-superconducting secondary phases act as intrinsic oxygen reservoir. Finally, when composition diverges even more from (2223) (CdSr >>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.

The effect of pre-sintering and deformation rate on critical current density behaviour of Bi-2223 bulk samples made by sinter forging

“…Although high J c of nearly 10 4 A cm −2 at 77 K has been reported for Bi-2223 bulks by several groups using the sinter forging technique for bulks of a small dimension [9,12], a quantitative relationship between J c and the deformation rate from sinter forging has been reported comparatively much less [7,13]. Also, J c values, ∼1000 A cm −2 , were obtained from small bulks with a cross-sectional area ∼0.1 mm 2 [7,8,13].…”

“…It is thus an effective method for significantly improving the texture of Bi-2223 material and results in an improvement of J c . The best J c achieved by this method is ∼10 4 A cm −2 at 77 K [9][10][11]. However, sinter forging has not been employed to fabricate large bulk samples by other groups working on high-T c superconductors.…”