ROLE OF PB SUBSTITUTION AND A STUDY OF SYNTHESIZING PROCEDURE FOR BI-BASED SUPERCONDUCTORS

Bulk superconductors of the (Bi1-xPbx)2Sr2Ca2Cu3Oy system have been synthesized by changing the Bi/Pb ratio. The effect of Pb substitution on T(c) has been studied by standard d.c. resistivity measurements. An appropriate thermal procedure and time for the preparation of the 110 K phase has also been studied at length. The experiments indicate that the best results are obtained for x = 0.2 and that a slow cooling process is necessary for a better control of the thermal process. Indexed X-ray diffraction patterns indicate the lattice parameters of low- and high- T(c) phases as a(L) = 0.54004 nm, b(L) = 0.5445 nm, c(L) = 3.084 nm and a(H) = 0.5483 nm, b(H) = 0.5339 nm, c(H) = 3.772 nm, respectively. The observed superconducting behaviour is stable on thermal cycling between 77 and 300 K.