Undoped Bi-2223 samples were prepared using a conventional solid-state reaction
method. Doping of Au in Bi-2223 was carried out by means of diffusion from an
evaporated Au film on pellets. We have investigated the effect of Au diffusion and
diffusion-annealing duration on the microstructure and superconducting properties of
Au-doped samples by performing x-ray diffraction (XRD), scanning electron microscopy
(SEM), dc resistivity and critical current density measurements. Gold diffusion in
Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy
has been studied over the temperature range
500–800 °C
using the technique of successive removal of thin layers and the measurements
of lattice parameters from XRD patterns at room temperature. The diffusion
doping of Bi-2223 by Au causes a significant increase of the lattice parameter
c
by about 0.19%. This observation is used for calculation of the Au diffusion coefficient in
Bi-2223. The Au diffusion coefficient decreases as the diffusion-annealing temperature
decreases. The temperature dependence of the Au diffusion coefficient in the range
500–800 °C is described
by the relation D = 4.4 × 10−4exp(−1.08 eV/kBT). Au doping of the sample increased the critical transition temperature and the critical current density
from 100 ± 0.2
to 104 ± 0.2 K and
from 40 to 125 A cm−2, in comparison with those of undoped samples. The critical transition temperature and critical
current density of Au-doped samples increased with increasing diffusion-annealing time from
10 to 50 h. Au doping of the sample also improved the surface morphology and increased the
high-Tc
phase ratio. The possible reasons for the observed improvement in superconducting
properties of the samples due to Au diffusion are discussed.