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

A factor of ∼ 1.5 enhancement in critical current I_c (at the I_c criterion of 0.01 μV/mm) of a Bi₂Sr₂Ca₂Cu₃O₁₀/Ag tape was observed by an introduction of a preheat treatment, 600°C for 6 h, prior to the final heat treatment at 840°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_c was associated with a sharpening of the resistive transition and with reductions in the specimen-to-specimen variations in I_c. Furthermore, it is suggestive that these improvements are primarily due to improved intergranular connectivity rather than to enhanced vortex pinning strength. The standard θ-2θ X-ray diffraction measurements on these specimens suggested that the ubiquitous high-Pb-containing precipitate, 3221, (Bi,Pb)₃Sr₂Ca₂CuO_x (or 531, (Sr,Ca)₅(Bi,Pb)₃CuO_x), 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.