The effects of adding fully reacted Bi-2223 seed particles on the phase transformation and microstructure of Ag/Bi-2223 tapes

The effect of adding fully reacted (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/ Cu/sub 3/O/sub y/ (Bi-2223) particles to the precursor powder on the final property of Ag/Bi-2223 tapes has been investigated. Different amounts of fully reacted Bi-2223 particles ranging from 0 to 10 wt% were added to the precursor powder consisting of mostly Bi-2212 and calcium plumbate phases. The tapes seeded with Bi-2223 particles showed a relatively high J/sub c/ in a short annealing time without mechanical deformation steps. The existence of Bi-2223 particles in the precursor powder resulted in a smaller grain size, showed no appreciable incubation period and a faster transformation rate in an isothermal annealing experiment compared to the tape containing no seed particles. A detailed analysis of the microstructure and phase transformation kinetics indicates that a two dimensional nucleation and growth process is the most plausible mechanism for Bi-2223 phase formation. For the tapes containing seed particles, the formation rate of Bi-2223 phase was found to be controlled by the diffusion of material, while the formation of nuclei controlled the Bi-2223 formation for the tape containing no seed particles.