Abstract:
Effect of introducing nano ZrO2 particles into (Ca,Sr)CuO2 added Bi 2223 superconductor composites is studied. Microstructures revealed that 20 mol. % (Ca,Sr)CuO2 phase added to Bi 2223 formed as micron sized particles among the Bi 2223 platelet shaped grains. Distribution of (Ca,Sr)CuO2 in Bi 2223 has enhanced the critical current density (Jc) and flux pinning force density (Fp ) substantially to fields up to 9 T at 20 K. Introduction of nano ZrO2 into the composite reacted with (Ca,Sr)CuO2 particles and formed additional secondary phases of increasing amount with a rise in ZrO2 content. This resulted in lowering of Jc(0) due to a gradual reduction in the fraction of superconducting phases, but retained the enhanced field range in which flux pinning was achieved. At 10 wt.% addition of ZrO2, Bi 2223 phase was suppressed, and Bi 2212 phase was promoted. Scaling behaviour of pinning force density has shown the dominant mechanism at low fields to be normal surface pinning due to interfacial defects. The fact that (Ca,Sr)CuO2 distributes itself as fine spherical particles in Bi 2223, without causing degradation of the superconducting matrix material, is of significance and opens up a scope to optimize the microstructures further for enhancement of flux pinning.
