Abstract:
Nano-tungsten trioxide (WO 3 ) particles were introduced homogeneously into Bi 1.2 Pb 0.3 Sr 1.54 Ca 2.06 Cu 3 O y (Bi 2223) superconductor matrix by a sol-casting technique and their effect on flux pinning properties was studied. To prevent W substitution at a lattice site of the matrix phase, WO 3 nanoparticles were added to processed Bi 2223 powders, which helped to retain transition temperature ( Tc ) near 105 K. The magnetic properties were obtained in the temperature ( T ) range of 10 to 77 K and up to 9 T magnetic fields ( B ). The temperature and field dependences of critical current densities ( Jc ) and the flux pinning force densities ( Fp ) were examined in terms of the possible sources of flux pinning in the samples. The addition of low concentrations (0.1 wt.%) of nano WO 3 led to effective pinning and enhancement of current densities to higher fields, up to 77 K, compared to Bi 2223. Analysis of Fp(B) curves showed normal surface pinning at platelet/grain boundary defects to be dominant at low fields at all temperatures, while additional pinning from WO 3 is observed at higher fields. The limiting fields where pinning from different mechanisms vanishes are estimated using scaling laws. Irreversibility fields ( B irr ) estimated from the high field region of Fp(B) curves suggest that substantial pinning is caused by nano WO 3 addition to Bi 2223.
