Comparison of superconducting properties of Ce added (Bi, Pb)-2212 with other rare earth additions

We have studied the effect of Ce addition on the superconducting properties of (Bi, Pb)-2212 and compared these properties with some of the important other rare earth (RE: La, Pr, Gd, Sm and Yb) additions in the system. The RE content was varied on a general stoichiometry of Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1RExOy. The samples were characterized by powder X-ray diffraction, SEM, R-T measurements and transport JC measurements at 64 K. It is known that addition of RE in general enhances the superconducting properties of (Bi, Pb)-2212 such as TC and JC. But in the case of Ce the maximum TC and JC are obtained at x = 0.1, a lower level comparing with those of the other REs for which the optimum concentration is x ≥ 0.2. The metal insulator (MI) transition also occurs at a lower concentration (x = 0.3) than the other rare earths, where it occurs at x > 0.5. The maximum values of TC and JC obtained in Ce addition are also lesser comparing with the other RE additions. These changes in the case of Ce addition comparing with the other REs are due to the tetravalent state of Ce in (Bi, Pb)-2212, whereas other REs are at trivalent state, and hence each Ce4+ substitution in place of Ca2+ and/or Sr2+ supplies more electrons in comparison with the other rare earths. Thus, in the case of Ce addition, the optimum carrier concentration of the system for maximum TC and JC attains at a lower level of addition than the other REs.