The critical current density and flux pinning properties of
Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1Oy
(where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) prepared by solid state synthesis in bulk polycrystalline
form were studied. The samples were characterized by powder x-ray diffraction
(XRD), scanning electron microscopy (SEM) equipped with energy-dispersive x-ray
analysis (EDS) and superconductivity measurements. The critical temperature
(TC), critical current
density (JC) and field
dependence of JC
of the Eu-substituted samples were found to be highly enhanced for optimum
doping levels. The peak position of the normalized pinning force density
(Fp/Fpmax) is found to shift to higher fields (0.88 T) for optimally doped samples
in contrast to 0.2 T for the undoped sample. The enhancement of the
JC–B characteristic and
pinning force density FP
(FP = JC × B) due to Eu substitution is of great technological significance.
The effect of Pr addition on the superconducting properties of the (Bi, Pb)-2212 system
in the bulk polycrystalline form was studied. The Pr content was varied from
x = 0.0 (pure) to 0.5 on a
general stoichiometry of Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1PrxOy. Phase analysis by XRD, microstructural examination by an SEM equipped with an energy
dispersive x-ray spectrometer (EDS), density measurements and superconductivity characterizations
were done to evaluate the relative performance of the samples. The critical current density
(JC)
and superconductivity transition temperature
(TC) of
Pr-added samples were found to be higher than that of the pure sample, i.e. without Pr added. A maximum
JC of
678.8 A cm−2 at 64 K was measured
for the sample with Pr = 0.2, which is more than seven times higher than that of the pure sample
(JC = 87.5 A cm−2). Also the
TC of the
sample with Pr = 0.2
was the highest (88.0 K) compared to all other samples. Microstructural examination
showed distinct variations in the grain morphology of the samples containing Pr, and the
porosity increases as the Pr content increases. Consequently, there is a significant
reduction in the density of the samples as the Pr content increases. A Sr-rich oxide
containing Pb(Bi) and Cu with square rectangular grains with rounded edges was
observed in the microstructure of Pr-added samples whose composition has been
analysed through EDS. But such a secondary phase could not be distinguished
from XRD analysis, probably due to the peak overlapping with (Bi, Pb)-2212.
The dependence of Ic on the bend strain and tensile stress
characteristics of (Bi, Pb)-2223/Ag-Cu alloy sheathed tapes with varying Cu
composition in the sheath has been studied in both mono- and multifilamentary
configurations. The irreversible stain (εr) and the critical
stress (σc) were found to improve as the level of Cu doping in the
sheath increases. εr and σc were found to be about twice
as large for the 9 at% Cu doped sample in both mono- and multifilamentary
cases compared to the corresponding pure samples. The multifilamentary tapes
were found to endure more strains and stresses due to their fine filament
structure and low fill factor of the superconductor core. The degradation of
Ic above σc was found to be rapid, while that for strains above
εr was gradual, retaining a significant amount of Ic even
after high values of applied strain.
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