Enhanced critical current in Bi2Sr2Ca2Cu3O10/Ag tapes by a low-temperature intermediate heat treatment

A factor of similar to 1.5 enhancement in critical current I-c (at the I-c criterion of 0.01 mu V/mm) of a Bi2Sr2Ca2Cu3O10/Ag tape was observed by an introduction of a preheat treatment, 600 degrees C for 6 h, prior to the final heat treatment at 840 degrees C in the fabrication process of the tape. This enhancement was also equally observed for tapes which were heat treated with substantially different temperature ramp rates for the final heat treatment. Perhaps, more importantly this increase in I, was associated with a sharpening of the resistive transition and with reductions in the specimen-to-specimen variations in I,. Furthermore, it is suggestive that these improvements are primarily due to improved intergranular connectivity rather than to enhanced vortex pinning strength. The standard theta-2 theta X-ray diffraction measurements on these specimens suggested that the ubiquitous high-Pb-containing precipitate, 3221, (Bi,Pb)(3)Sr2Ca2CuOx (or 531, (Sr,Ca)(5)(Bi,Pb)(3)CuOx), appeared to play a significant role in these enhancements by precipitating during the preheat treatment and melting as the temperature is raised to the reaction temperature. (C) 1998 Elsevier Science B.V. All rights reserved.