Preparation of the textured Bi-based oxide tapes by partial melting process

Abstract

Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ textured tapes with an excellent J/sub c/ were prepared by doctor-blade casting and a partial melt process. A green tape, composed of Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ powder and an organic formulation, was laid on a silver foil and heat-treated. A highly textured microstructure was formed during slow cooling between 890 degrees C and 870 degrees C. X-ray diffraction and scanning-electron-microscope observation indicated that initially an oriented Bi/sub 2/Sr/sub 2/Cu/sub 1/O/sub x/ structure forms by growth from the melt, and it subsequently transforms to the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ phase. A grain alignment was significantly enhanced in the oxide layer with a thickness less than 20 mu m. Silver dissolved in the oxide from the substrate also plays an important role in the grain alignment by lowering the melting point of the oxide. The T/sub c/ of a tape could be increased to 89 K by quenching from 870 degrees C. The J/sub c/ was 1.3*10/sup 4/ A/cm/sup 2/ at 77 K, 0 T and 1.4*10/sup 5/ A/cm/sup 2/ at 4.2 K in a high magnetic field of 25 T.