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.

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The enhanced critical current density (JC) and flux pinning properties of Bi1.7Pb0.4Sr2-xGdxCa1.1Cu2.1O8+δ (where x=0.0, 0.1, 0.2, and 0.3) system prepared by solid-state synthesis in bulk polycrystalline form were studied. Phase analysis, microstructural investigation, and superconducting characterization were performed to evaluate the relative performance of the samples. The x-ray diffraction and energy dispersive spectroscopy analyses show that Gd atoms are successfully doped in place of Sr in the system. It is found that Gd in (Bi, Pb)-2212 enhances the critical temperature (TC), JC, and flux pinning strength of the system. The flux pinning force (FP) calculated from the field dependant JC values shows that the irreversibility line of the Gd-doped (Bi, Pb)-2212 shift toward higher fields to different extents depending on the value of x. The samples with x=0.2 show maximum FP of 645 kN m−3 and the peak position of FP shifts to higher fields (0.68 T) as against 26 kN m−3 and 0.12 T for the pure sample. Also, the values of self-field JC and pinning potential (U0) are maximum for this sample (x=0.2). The enhancements of TC, self-field JC, JC(B) characteristics, U0, and FP are explained on the basis of the hole optimization and formation of point defects due to the doping of Gd in (Bi, Pb)-2212 system.