Studies of the Bi(2223) phase formation mechanism in Pb substituted and Pb free bulk samples and in Ag sheathed tapes

From the study of the Bi(2223) phase formation mechanism on pressed pellets of the Pb stabilized (Bi,Pb)2Sr2Ca2Cu3O10+d compound it was concluded that a nucleation and growth mechanism is suitable to describe the transformations occurring in air. This was concluded from observation by SEM of the transformations occurring on a fixed location at the surface of a pellet after several heat treatments at the reaction temperature, 852°C. The same type of investigation, carried out on the compound Bi2Sr2Ca2Cu3010+δ without Pb led to the same conclusions as for the case containing Pb, the only difference being a higher reaction temperature, 879°C. Finally the study was extended to Ag sheathed Bi,Pb(2223) tapes. In the last case, the phase formation was investigated using transmission electron microscopy after several reaction times at 840°C. Here a stacking-sequence analysis was carried out, based on the lattice-fringe images taken from a total of 108 grains, where 36 grains were randomly chosen after each of the three heating times, e.g. 9, 17 and 25 hours, respectively. From all these observations it follows that the formation of the Bi(2223) phase occurs simultaneously with a gradual decomposition of the Bi(2212) platelets initially present in the mixture. In addition, it can be concluded that the Bi(2223) phase primarily forms via a nucleation and growth process