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 obser ved 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 ta pes which were heat treated with substantially different temperature r amp rates for the final heat treatment. Perhaps, more importantly this increase in I, was associated with a sharpening of the resistive tran sition 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 vo rtex pinning strength. The standard theta-2 theta X-ray diffraction me asurements on these specimens suggested that the ubiquitous high-Pb-co ntaining precipitate, 3221, (Bi,Pb)(3)Sr2Ca2CuOx (or 531, (Sr,Ca)(5)(B i,Pb)(3)CuOx), appeared to play a significant role in these enhancemen ts by precipitating during the preheat treatment and melting as the te mperature is raised to the reaction temperature. (C) 1998 Elsevier Sci ence B.V. All rights reserved.