Evidence for enhanced grain connectivity due to second phase reduction of Bi-2223/Ag tapes

Processing of Bi-2223/Ag tapes in a three-stage sintering process with reduced last processing temperature and intermediate cooling to room temperature leads to enhanced critical current densities. X-ray diffraction analysis shows that this is accompanied by the reduction of second phases like Bi-2201 and Bi-3221 in the superconducting core. Electron microscopy exhibits that these phases tend to precipitate between the Bi-2223 grains, where they can hinder the current path. The results are compared with those of a previously reported two stage sintering procedure. A complicated reaction between 3221, alkaline earth cuprates, Bi-2212 and Bi-2223 is proposed as a tentative explanation for the reduction of 3221.