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

Bi₂Sr₂Ca₁Cu₂O_x textured tapes with an excellent J_c were prepared by doctor-blade casting and a partial melt process. A green tape, composed of Bi₂Sr₂Ca₁Cu₂O_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°C and 870°C. X-ray diffraction and scanning-electron-microscope observation indicated that initially an oriented Bi₂Sr₂Cu₁O_x structure forms by growth from the melt, and it subsequently transforms to the Bi₂Sr₂Ca₁Cu₂O_x phase. A grain alignment was significantly enhanced in the oxide layer with a thickness less than 20 μm. 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_c of a tape could be increased to 89 K by quenching from 870 °C. The J_c was 1.3×10⁴ A/cm² at 77 K, 0 T and 1.4×10⁵ A/cm² at 4.2 K in a high magnetic field of 25 T