Diffusion coefficient, activation energy and the effect of Ag-doping on some physical properties of silver doped Bi1.8Pb0.4Ca2.2Sr2Cu3Ox

The aim of the present study is to investigate the effect of diffusion-doped silver on some physical properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox superconducting samples and to calculate the diffusion coefficient and the activation energy of silver. The present work consists of three parts: (a) optimization of annealing temperature, (b) the effect of Ag diffusion-doped on microstructure and superconducting properties of Bi(Pb)CaSrCuO, and (c) calculation of diffusion coefficient of silver. First, to investigate the optimum annealing temperature we prepared Bi1.8Pb0.4Ca2.2Sr2Cu3Ox ceramic superconductors annealed at 830, 835, 840, 845, and 850 deg. C using the solid state reaction method. The investigations consist of XRD, SEM, dc resistivity, and transport critical current density measurements. The highest Tc and Jc values were observed for the sample annealed at 840 deg. C for 48 h (B840). Large grain size, denser surface, and high volume fraction of the high-Tc phase were obtained for the sample B840. The diffusion doping of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox by silver increased the critical current density from 123 to 696 A/cm2 and the transition critical temperature by about 3 K compared with the undoped sample. Ag-doping increased the amount of high-Tc phase and improved the surface morphology. It also caused an increase of the lattice parameter c by an amount of 0.15%. The temperature dependence of the silver diffusion coefficient in the range 600-800 deg. C is described by D=2.9x10-4exp(-1.05 eV/kBT). Possible reasons for the observed improvement in the structural and superconducting properties of the samples due to silver diffusion are discussed.