Preparation and degradation behaviour of Bi-cuprate superconductors

Abstract

The role of preparation conditions and the effect of addition of Pb in Bi-Sr-Ca-Cu-O (BSCCO) superconductor, on theT_c, J_c and grain orientation have been studied. Calcination at a temperature higher than the melting point of Bi₂O₃ after the prereaction at 800° C leads to formation of c-axis oriented nearly single phase material. The presence of lead yields a nearly high T_c phase (2223) exhibiting a maximum transition temperature T_c=110 K and Δ T_c=2 K. The addition of lead and grain orientation together result in an increase in J_c by nearly two orders of magnitude. The degradation behaviour was studied in terms of changes in T_c, J_c and structure on exposure to atmosphere up to 250 days. Samples with 0.6 Pb were found to be superconducting with T_c=97 K even after 250 days. The high T_c phase was stable against degradation. Our studies indicate that the degradation of leaded BSCCO is a surface phenomenon rather than bulk phenomenon.