Enhanced flux pinning of an nd-added (Bi,Pb)-2212 superconductor

Abstract

The flux pinning properties of a (Bi,Pb)-2212 superconductor by the addition of a rare-earth element Nd with varying concentrations were studied. The Nd content of the samples was varied from x=0.0 to 0.5 on a general stoichiometry of Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1NdxOy. The samples were characterized by powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and transport critical current measurements at 64 K. Both self-field J(C) and J(C) in the presence of an applied magnetic field (J(C)-B) of Nd-added samples were found to be much better than those of the pure sample. Also, the peak values of the bulk pinning force density (F-Pmax) of Nd-added samples shift toward higher magnetic fields, indicative of the enhanced flux pinning strength of the samples. The results are explained based on the replacement of cations such as Sr2+, Ca2+, and Bi3+ by Nd3+ ions and the associated distortion of the lattice and change in hole concentration in the system. The replacement produced point-like defects due to the difference in the ionic radii of Sr2+ (1.12 angstrom), Ca2+ (0.99 angstrom), Bi3+ (0.96 angstrom), and Nd3+ (1.04 angstrom). The nanoscale secondary phase precipitates produced due to Nd addition may also act as flux pinners.