Formation of nucleation centers for vortices in Bi-2223 superconducting core by dispersed Sn nanoparticles

摘要

In this study, we investigate the effect of the Sn diffusion at different annealing temperature in the range of 650-850 °C on the microstructural, electrical, mechanical and superconducting properties of the Bi_(1.8)-Pb_(0.4)Sr_(2.0)Ca_(2.1)Cu_(3.0)O_y materials prepared by the standard solid state reaction method with the aid of bulk density, dc resistivity (p-T), transport critical current density (J_c), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers microhardness (H_v) measurements. It is found that all the properties given above are significantly dependent upon both the Sn nanoparticles inserted in the Bi-2223 superconducting matrix and diffusion annealing temperature. Namely, the dc resistivity measurements indicate that all the samples exhibit the metallic behavior as a result of the electron-phonon interaction in the Bi-2223 crystal structure or logarithmic divergence in density of states at the Fermi level. Further, the normal state resistivity decreases with the enhancement of the annealing temperature owing to the increment of the metallic connection between the superconducting grains due to the optimization of the hole density and possible changes in the lattice vibration. Likewise, onset and offset critical transition temperature values tend to enhance with the diffusion annealing temperature, confirming not only the improvement of crystallinity and especially connectivity between the superconducting grains but the increment in the average grain size and mobile hole concentration in the Cu-O_2 slabs of the Bi-2223 system, as well. The decrement in the degree of the broadening stems from the degradation of the porosity,