PHASE EVOLUTION IN SILVER-DOPED BIPBSRCACUO(2223)/AG SUPERCONDUCTING COMPOSITES

Silver doping into (Bi, Pb)2Sr2Ca2Cu3O10 superconducting composite tapes was found to accelerate the formation process of high-T(c) (2223) phase owing to lowering the partial melting point of the samples. The differential thermal analysis (DTA) results showed that the partial melting temperature of the sample was lowered by about 10-degrees-C from 850-degrees-C to 840-degrees-C by silver doping. However, with sufficient sintering both the silver-doped and undoped samples can reach a very high level of high-T(c) phase fraction, suggesting that the silver doping only speeds up the rate of high-T(c) phase formation, but does not change the final phase assemblage of the materials. The reaction kinetics was analyzed by using the Avrami equation, and the results indicated that the conversion process of low-T(c) (2212) phase to high-T(c) (2223) phase was a diffusion-controlled, two-dimensional reaction. The correlation of the phase evolution with electrical property inside the superconducting tape during the process of heat treatment was also discussed.