Enhanced flux pinning in (Bi,Pb)-2223/Ag tapes by slight Ni doping

Abstract

Bi-2223/Ag tapes with nominal chemical compositions of Bi 1.8Pb 0.4Sr 2Ca 2.2Cu 3− x Ni x O y ( x=0, 0.003 and 0.005) were prepared by powder-in-tube method. The XRD and SEM analysis of their phases and microstructures show that a proper amount of Ni doping at Cu sites does not impede the formation of Bi-2223 phase. The measurements of magnetic field dependence of critical current density J c and resistance transition broadening under magnetic fields oriented along c-axis indicate that the Ni doping at Cu site can improve the flux-pinning ability of Bi-2223/Ag tapes significantly. The improvement of flux pinning is suggested to originate from the introduction of flux pinning centers due to the destruction of local superconductivity caused by Ni doping at Cu sites because of the ferromagnetism of Ni.