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

Abstract

The crystallization mechanism of an amorphous Bi2Sr2Ca2Cu3Oy 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 Bi2Sr2Ca2-xCdxCu2Oy 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 Bi2Sr2Ca2-xCdxCu3Oy 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.