J. Khaled et al., A NEW MODEL FOR THE FORMATION OF HIGH-T-C PHASE IN SUPERCONDUCTIVE (BI, PB)(2)SR2CA2CU3OX GLASS-CERAMICS, Journal of materials science. Materials in electronics, 7(4), 1996, pp. 261-266
The formation mechanism of the high-T-c phase through the glass-cerami
c route and the role of Pb on the formation of this phase have been in
vestigated. It was found that a new compound with the chemical composi
tion Pb2Sr3-xCaxCuOy (x=1.8) precipitates at around 550 degrees C. Thi
s phase is stable up to 800 degrees C, where it begins to decompose, a
nd at 850 degrees C it completely disappears. It was found that some p
art of the released Pb diffuses into the 2212 phase leading to the for
mation of Pb-containing 2212 phase, (Bi,Pb)(2)Sr2CaCu2Ox. On the other
hand, an endothermic peak, probably arising from the melting of (Bi,P
b)(2)Sr2CaCu2Ox phase or melting at grain boundaries containing Pb2+,
was observed at 856 degrees C only in Pb-containing samples that were
heat treated. The liquid phase attributed to the endothermic peak may
enhance the formation of high-T-c phase (2223 phase). The growth kinet
ics for the high-T-c phase were analysed using the Johnson-Mehl-Avrami
equation; the results indicate that the growth of the high-T-c phase
is controlled by a diffusion process and the activation energy for its
formation in the initial stage (shorter than 96 h) is 576+/-45 kJ mol
(-1).