Synthesis of Bi-base high-Tcoxides through a diffusion reaction

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Abstract
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 Tc of 109 K. Referring to the predominant (100) texture, the most favourable direction for current transfer seems to be in the diffusion direction.