HIGH-T-C SUPERCONDUCTIVITY IN BI1.6PB0.4SR2CA2 CU2+XOY COMPOUNDS

Superconducting samples with the nominal composition Bi1.6P0.4Sr2Ca2Cu 2+xOy (x = 1.6, 1.81, 2.0) have been prepared by a solid state reactio n technique. The resistivity data reveal the occurrence of multiphases in all the samples. By a process of ageing over 2 years then reanneal ing, a dramatic increase in T-c was observed in the above system for x = 2.0. We achieved zero resistance at 130 K, which is the highest in the composition Bi1.6Pb0.4Sr2Ca2Cu2+xOy (x = 1.6, 1.8, 2.0) reported s o far but the recipe is often not reproducible. This shows that the sy stem is sensitive to Cu composition and to the conditions of preparati on. Furthermore, long storage leads to a detoriation in the supercondu cting properties. X-ray diffraction studies show that these samples ma inly contain the (2223) phase. However, in each sample, a few lines co uld not be indexed, which may indicate the presence of some new phase.