Crystallization process of Bi-containing superconductors prepared from rapidly quenched amorphous materials and effects of CdO addition on the process

The crystallization mechanism of an amorphous Bi₂Sr₂Ca₂Cu₃O_y phase was studied from the relations between crystallization and volume changes by dilatometry. Further, the effect of addition of CdO on the crystallization mechanism and superconductivity was discussed. The glass transition and crystallization temperatures for the amorphous phase with composition of Bi₂Sr₂Ca_2-xCd_xCu₂O_y were between 420° and 360°C, and between 440° and 420°C, respectively. Both values tend to decrease with increasing CdO content. The shrinkage of the amorphous Bi₂Sr₂Ca_2-xCd_xCu₃O_y phase occurred with the crystallization of a c₀=2.5 nm phase. Furthermore, the amount of the c₀=2.5 nm phase decreased with increasing CdO content with a minimum at x = 0.4. Better superconductivity was obtained in the specimens containing less amount of the c₀=2.5 nm phase.