Preparation of superconducting Bi-Sr-Ca-Cu-O ceramics by the sol-gel method

Abstract

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 Bi₂Sr₂CaCu₂O_x 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 Bi_1-x Sr_xO_y (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi₂Sr₂CaCu₂O_x phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT _c (end) in the gel of molar composition Bi∶Sr∶Ca∶Cu = 2∶2∶2∶3, while a slow cooling increasedT _c (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 showedT _c (onset) at 115 K andT _c (end) at 105K.