THE KINETIC RELATIONSHIPS AND ACTIVATION-ENERGY OF BI-BASED SUPERCONDUCTING PHASE-FORMATION

In this paper, the kinetic relationships with regard to the formation of 2212 and 2223 superconducting phases have been studied for a Bi-bas ed superconductor with 2223 nominal composition. The formation of the Pb-doped 2223 phase and the 2212 phase with or without Pb obey the nuc leation and crystal growing model, whose kinetic equations are Q(i) = 1-exp(-K(i)t(n)), whereas the formation of 2223 phase in the Pb-free s ystem belongs to the nucleus boundary shrinking model, and the equatio n is 1 - (1 - Q2223)1/3 = K2223t. It is proved that the factor control ling phase formation is the activation energy of the overall reaction. The optimum sintering temperature range for the formation and the tra nsformation relationships between the high-temperature phase and low-t emperature phase are discussed.