Flux pinning improvement in Bi-2212 silver sheathed tapes with submicron SrZrO3 inclusions

Silver sheathed tapes of Bi-2212 undoped and doped with SrZrO 3 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 3 addition. The doped samples contain SrZrO 3 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 SrZrO 3 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°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 SrZrO 3 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.