The effect of Ag-doping on the magnetic behaviour of Bi-(Pb)-Sr-Ca-Cu-O ceramic superconductors

AC susceptibility chi'(T, H-ac) and chi "(T, H-ac) measurements have been carried out on rectangular bar shaped high-temperature superconductors with nominal composition of Bi1.6Pb0.4Sr2Ca3Cu4-xAgxO12 (x=0-1.0) prepared by the solid state reaction method. The effect of Ag-doping on the Bi-(Pb)-Sr-Ca-Cu-O system has been investigated in terms of an AC susceptibility study. It was found that as the amount of Ag doping increases, the critical current density decreases. We also qualitatively discuss experimental results in the framework of the critical state model (CSM). Comparison of the observations and the results of the CSM suggests the Bean like dependence of the intergrain (matrix) depinning critical current density j(cm) on the magnetic flux density B in the low field range studied. The temperature dependence of the pinning strength parameter alpha(T) obtained from AC dissipation is in good agreement with the relation alpha=alpha(0)(1-T/T-C)(2.37) for undoped Bi-(Pb)-Sr-Ca-Cu-O. (C) 1998 Elsevier Science S.A.