FLUX-PINNING IMPROVEMENT IN BI-2212 SILVER-SHEATHED TAPES WITH SUBMICRON SRZRO3 INCLUSIONS

Silver sheathed tapes of Bi-2212 undoped and doped with SrZrO3 have been prepared, using co-precipitated oxalates as precursors. Thermal treatment conditions have been optimised, varying the maximum processing temperature T-max. A comparative study on thermal treatment conditions, microstructure, and flux pinning properties for doped and undoped samples has been performed in order to evaluate the effect of SrZrO, addition. The doped samples contain SrZrO, submicron particles, appearing as aggregates included between Bi-2212 lamellae with a Cu-free phase and the rest of the liquid, and also distributed inside Bi-2212 grains. The presence of SrZrO3 surplus leads to higher critical current densities in samples prepared in a wide T-max range; in addition, the lowest T-max at which high J(c) can be obtained, becomes 5 deg lower (875 degrees C). At T = 5 K critical currents for all the samples are of the order of 10(5) A/cm(2) and are independent of doping, while at 60 K doped samples exhibit roughly two times higher J(c) in zero field and more than an order of magnitude higher J(c) at H = 40 mT. A magnetisation decay study reveals that samples with SrZrO3 surplus have a larger fraction of pinning centres with high energy. The enhanced pinning properties can be related to the finely dispersed zirconate inclusions found in the superconductor matrix.