PREPARATION OF SUPERCONDUCTING BI-SR-CA-CU-O CERAMICS BY THE SOL-GEL METHOD

Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi2Sr2CaCu2Ox phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C4H6O6/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition Bi:Sr:Ca:Cu = 2:2:2:3 was decomposed to CaCO3, CaO, CuO and Bi1-x SrxOy (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi2Sr2CaCu2Ox phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increased Tc (end) in the gel of molar composition Bi:Sr:Ca:Cu = 2:2:2:3, while a slow cooling increased Tc (end) in the lead-containing gel of molar composition Bi:Pb:Sr:Ca:Cu = 1.85:0.35:1.9:2.0:3.1. The latter showed Tc (onset) at 115 K and Tc (end) at 105K. © 1990 Chapman and Hall Ltd.