SYNTHESIS OF BI-BASE HIGH-TC OXIDES THROUGH A DIFFUSION REACTION

Bi-base high-Tc 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 Bi2Sr2CaCu2Ox. 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 Tc obtained is 78 K. The Jc 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.