Undoped Bi-2223 samples were prepared by using a conventional solid-state reaction method. Doping of Au into Bi-2223 was carried out by means of diffusion from an evaporated Au film on pellets. An investigation was made, of the effect of Au diffusion and diffusion-annealing time upon the microstructure and superconducting properties of Au-doped samples, by performing X-ray diffraction, scanning electron microscopy, direct-current resistivity and critical current density measurements. The Au diffusion in Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy was studied at 500 to 800C by using the technique of successive removal of thin layers and measurements of lattice parameters deduced from X-ray diffraction patterns at room temperature. The diffusion doping of Bi-2223 with Au caused a significant increase in the lattice parameter of about 0.19%. This observation was used to calculate the Au diffusion coefficient in Bi-2223. The Au diffusion coefficient decreased as the diffusion-annealing temperature was decreased. The temperature dependence of the Au diffusion coefficient at 500 to 800C was described by:

D (cm2/s) = 4.4 x 10-4 exp[-1.08(eV)/kT]

The Au-doping of the sample increased the critical transition temperature and the critical current density from 100 to 104K, and from 40 to 125A/cm2, in comparison with the values for undoped samples. The critical transition temperature and the critical current density of Au-doped samples increased with increasing diffusion-annealing time from 10 to 50h. The Au-doping of the sample also improved the surface morphology and increased the high-Tc phase ratio.

Calculation of the Diffusion Coefficient of Au in Bi-2223 Superconductors. O.Ozturk, T.Küçükömeröglu, C.Terzioglu: Journal of Physics - Condensed Matter, 2007, 19[34] 346205 (10pp)