Improvement of the intergranular pinning energy in the Na-doped Bi-2212 superconductors

In the present study, magnetoresistivity performance of polycrystalline Bi₂Sr₂Ca_1−x Na _x Cu₂O_8+y superconductor with x = 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 has been studied by change of flux pinning mechanism. Samples have been prepared using a polymer solution technique with polyethyleneimine. The effects of Na substitution for Ca on the activation energies, irreversibility field, upper critical magnetic field and coherence length have been studied. The magnetoresistance of samples has been measured at applied magnetic fields between 0 and 9 T. Broadening of superconducting transition has been observed under magnetic field, explained on the basis of Thermally Activated Flux Flow (TAFF) model. The upper critical magnetic field H _C2 (0) and the coherence length (ζ(0)) at T = 0 K were calculated using the resistivity data and H _C2(0), respectively. H _C2 (0) and ξ(0) values have been calculated as 186.4, 195.5, 321.0, 296.0, 292.5, 280.9 T, and 13.29, 12.98, 10.13, 10.55, 10.61, 10.69 Å for the 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 Na-doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi₂Sr₂Ca_1−xNa_xCu₂O_8+y where x = 0.075 determined to be 0.019 eV for 9 T and 0.239 eV for 0 T.