Enhancement of superconducting properties of Bi-based oxide high T_c thick films using nanosized crystals as flux-pinning centers

The use of nanosized crystals as flux-pinning centers to improve the critical current density (J_c) - magnetic field (H) dependence of Bi-oxide high transition temperature (T_c) superconducting thick films was studied. It is demonstrated that the controlled introduction of (Sr, Ca)₁₄Cu₂₄O_41+x needle-like defects into Bi₂Sr₂CaCu₂O_8+x/Ag composite tapes improved the J_c in magnetic fields from 0 to 1 T from 20 - 60 K. The experimental data was also consistent with the inclusion flux-pinning model J_c = Const V_f/d, where the critical current density increases as the defect size is reduced or the volume fraction of defects is increased.