Investigation of some physical properties of gold diffusion-doped Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$O$_{y}$ superconductors

We have investigated the effect of the gold-diffusion doped Bi-2223 superconducting samples on the crystal structure and superconducting properties using XRD, SEM, T$_{c}$, J$_{c}$, and room temperature resistivity measurements. Doping of Bi-2223 was carried out by means of gold diffusion from an evaporated onto pellets at the sintering. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters calculations and grain size, respectively. The gold diffusion in the Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$O$_{y}$ has been also studied over the temperature range 500-800 $^{^{\circ}}$C$_{ }$using the technique of successive removal of thin layers and measurement of the sample resistivity at room temperature. The temperature dependence of the Au diffusion coefficient in the range 500-800 $^{^{\circ}}$C was described by the relation D=4x10$^{-4}$exp(- 1.08 eV/k$_{B}$T). For the Au-doped sample, the critical transition temperature and J$_{c}$ were increased from 100$\pm $1 K to 104$\pm $1 K and from 40 and 125 A cm$^{-2}$, respectively, in comparison with those of undoped Bi-2223. The possible reasons for the observed increases in critical temperature and critical current density due to Au diffusion were discussed.