Synthesis of Bi-base high-T_c oxides through a diffusion reaction

Bi-base high-T_c oxides have been prepared by diffusion process where diffusion couples composed of a Bi-base oxide and a Sr-base oxide were reacted. In the specimen reacted at 840 degrees C for 80 h a diffusion layer approximately 150 mu m thick with nearly uniform composition has been formed. An EPA analysis has revealed that the composition of the diffusion layer corresponds to Bi₂Sr₂CaCu₂O_x. A SEM structure taken on a fractured surface of the cross section of the diffusion layer is composed of columnar grains grown parallel to the diffusion direction. A significant (100) texture has been observed in the X-ray diffraction pattern taken on the surface of the diffusion layer. The highest offset T_c obtained is 78 K. The J_c of the diffusion layer calculated from the magnetisation is 6*10⁵ A cm^-2 at 4.2 K. A partial substitution of Pb for Bi in the diffusion component yields an offset T_c of 109 K. Referring to the predominant (100) texture, the most favourable direction for current transfer seems to be in the diffusion direction.