A FORMATION MECHANISM OF BI-2223 BY MIXING INTERMEDIATE COMPOUNDS IN THE BI(PB)-SR-CA-CU-O SYSTEM

Abstract

The formation and growth behaviour of the Bi-2223 phase was investigated by sintering a mixture of Bi0.82Cu0.18Ox, Sr2CuO3, Ca2CuO3, CuO and PbO at 850 degrees C. The mixture was partially melted at 770 degrees C because of the eutectic liquid from Bi0.82Cu0.18Ox. The liquid phase was unable to directly synthesize the Bi-2223 phase from the mixture. instead, it enhanced the formation of the Bi-2212 phase with large grains. Then the Bi-2223 phase seemed to form both at the grain boundaries and on the free surfaces of the Bi-2212 phase and grew along the ab planes of the Bi-2223 phase with the dissolution of the Bi-2212 phase, resulting in larger Bi-2223 platelets than those in the conventional process which requires the calcination of a mixture of Bi2O3, SrCO3, CaCO3, CuO and PbO. This new mixture also enhanced the transformation rate from the Bi-2212 phase to the Bi-2223 phase. Our results indicated that the formation of the Bi-2212 and Bi-2223 phases was a consecutive reaction and larger Bi-2223 platelets could be prepared by sintering at 850 degrees C with a mixture of intermediate compounds in the Bi(Pb)-Sr-Ca-Cu-O system.