Flux pinning properties of rare earth modified (Bi, Pb)-2212 superconductors

The flux pinning properties of (Bi, Pb)-2212 superconductors modified by the addition of rare earth (RE) elements La, Gd and Yb with varying concentrations are studied. Samples were prepared by a conventional solid state route with initial stoichiometry of Bi1.7Pb0.4Sr2Ca1.1Cu2.1RExOy (where RE = La, Gd, Yb and x = 0.0 (pure), 0.1, 0.2, 0.3, 0.4). The samples were characterized by powder x-ray diffraction, scanning electron microscopy, R–T measurements and superconductivity measurements at 64 K. It is found that the addition of these elements considerably enhances the flux pinning strength of the system, and there is also an increase of critical temperature (TC) and critical current density (JC). These values become maximum at optimum concentrations (x = 0.2–0.3), and at higher levels of addition, these values decrease. The results are explained based on the replacement of Sr2+ and/or Ca2+ by RE3+ ions and the associated distortion of the lattice and change in carrier concentration of the system. La and Yb are found to be more effective than Gd in obtaining better flux pinning properties.