SYNTHESIS OF HIGH-TC SUPERCONDUCTING BI-PBSR-CA-CU-O CERAMICS PREPARED BY AN ULTRASTRUCTURE PROCESSING VIA THE OXALATE ROUTE

The oxalate precursor yielded by a sol-gel processing can be pyrolysed and oxidized at 840 ° C for 40h into the desired high-Tc superconductor in the lead-doped Bi-Sr-Ca-Cu-O system with Tc(onset) = 140 K and Tc(zero) = 104K. The mechanisms of the sol-gel reaction were monitored by analysis of Fourier transformation infrared (FTIR) spectroscopy. Moreover, identification of the various phases existing on the specimens after firing at selected temperatures, was made by analysis by FTIR spectroscopy and X-ray diffractometry. Based on the experiment results, the mechanisms of forming Bi2Sr2CaCu2O8+δ (phase 2212) might be identified as the reaction of Bi2Sr2CuO6+δ, Ca2CuO3 and CuO at 800 ° C. Furthermore, Bi2Sr2Ca2Cu3O10+δ (phase 2223) might be synthesized by the reaction of phase 2212, Ca2CuO3 and CuO at 840 ° C. Ca2PbO4 found in lead-doped materials may catalyse the formation reaction of Ca2CuO3 at 650 ° C and play a role of a flux to fuse Bi2Sr2CaCu2O8+δ, CuO and residual Ca2CuO3 and then improve the further synthesis of Bi2Sr2Ca2Cu3O10+δ at 840 δ C. © 1990 Chapman and Hall Ltd.