The effect of Au diffusion on some physical properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

We have investigated the effect of the gold diffusion on the crystal structure and superconducting properties of Bi-2223 superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), critical transition temperature, critical current density, and room temperature resistivity measurements. Doping of Bi-2223 was carried out by means of gold diffusion from an evaporated gold film on pellets during sintering. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size, respectively. Au doping of the samples 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 gold diffusion in Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy has been studied over the temperature range of 500-830 degrees C using the technique of successive removal of thin layers and measurement of the sample's conductivity at room temperature. The temperature dependence of the Au diffusion coefficient in the range of 500-830 degrees C was described by the relation D = 5 x 10(-4) exp (-1.09 eV/kBT). The possible reasons for the observed improvements in microstructure and superconducting properties due to Au diffusion were discussed. (c) 2008 Elsevier B.V. All rights reserved.