A comparative study of rapid and slow furnace cooling effects on the superconducting properties of Pb-free and Pb-doped Bi-2212 HTSC

A study of the Pb-doped Bi-2212 phase in comparison to that of the Pb-free Bi-2212 phase under two different conditions: (i) rapid cooling (RC) and furnace cooling (FC), and (ii) variation of sintering time from 12 to 144 h has been carried out. The Pb-doped samples showed a change, while the Pb-free samples did not show any change in the superconducting behaviour with increasing sintering time under identical conditions of RC and FC. For all the sintering durations, the Pb-free samples always showed T c(FC) > T c(FC), while the Pb-doped samples showed the opposite trend, that is, T c(RC) < T c(FC) for shorter sinterings (12 to 36 h), whereas, an identical trend, that is, T c(RC) > T c(FC) for longer sinterings (48 to 144 h). Detailed XRD, TEM, SEM and EDAX studies suggest that this changing behaviour of the Pb-doped Bi-2212 samples may probably be due to changes occurring in the band structure and in the microstructure affecting electronic properties of the material depending upon the site occupied by Pb under RC and FC regimes, with increasing sintering time.