Effect of grain network modifications due to additives on critical current (I<inf>c</inf>) in Bi-2212 superconductor

The presence of weak links in high-Tc superconductors is a major drawback in achieving high critical current densities. The present study deals with the effect of additives (Ag, Ag2O and BaBiO3) on the weak link behaviour of Bi-2212 in bulk form. It is observed that the addition of silver (Ag) metal powder improves the connectivity between the grains by proximity-effect and thereby enhances the current carrying capability at temperatures very close to Tc. De Gennes and Clarke models have been invoked to establish that Bi-2212 containing insulating additives (BaBiO3 and Ag2O) show a superconductor-insulator-superconductor (S-I-S) type grain network and thereby enhance the weak link behaviour, whereas metallic Ag addition shows a superconductor-normal metal-superconductor (S-N-S) behaviour and is, therefore, a potential candidate for large scale applications. Further support to this data is obtained from ac susceptibility studies carried out at different magnetic field strengths (0.1-4.0 Oe).