Nonreactive Nano WO3 Inclusions to Enhance Flux Pinning in Bi-2223 Superconductor Composites

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 (
T_c
) 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 (
J_c
) and the flux pinning force densities (
F_p
) 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
F_p(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
F_p(B)
curves suggest that substantial pinning is caused by nano WO
₃
addition to Bi 2223.