THERMAL-PROCESSING OF CERAMIC SUPERCONDUCTORS IN THE SYSTEM BI-CA-SR-CU-O

Superconductors in the system Bi-Ca-Sr-Cu-O were prepared from mixtures with initial cation proportions of 1111 and 6356. The effects of heat-treatment conditions, particularly, temperature, atmosphere, and cooling rates, on diamagnetic transition characteristics, were investigated. Calcined powders were found to be comprised primarily of the '2122 phase'. The transition temperature associated with this phase was determined to range from 60-80 K, depending upon the thermal processing conditions. By contrast with YBa//2Cu//3O//7// minus // delta , the superconducting transition temperature, T//c, was found to (i) decrease on annealing in oxygen and (ii) increase with increasing cooling rate in air. The increase in T//c observed for rapid cooling and quenching was related to an oxygen deficiency effect rather than to the cooling rate per se. An additional phase associated with a higher transition temperature of 112 K was present in all samples.