The effect of Ag diffusion on properties of BiPbSrCaCuO thin films

Superconducting BiPbSrCaCuO films have been evaporated on Ag/MgO and MgO substrates (with and without Ag buffer layer) by the electron-beam technique. The influence of annealing temperature on the crystalline structure and superconducting properties of BiPbSrCaCuO films was investigated by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, critical temperature, critical current density and room temperature resistivity measurements. It was shown that the annealing of both types of films at 835 degrees C or 845 degrees C resulted in formation of the mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c-axis perpendicular to the substrates. Annealing of films on Ag/MgO substrates is additionally accompanied by Ag diffusion from the buffer layer into BiPbSrCaCuO films. The higher rate of crystallization of the Bi-2223 and Bi-2212 phases, the higher degree of c-axis orientation, the higher dense surface morphology, the reduced lattice parameter c (by 0.6-0.8%) the reduced room temperature resistivity (2-3 times), the significantly enhanced critical temperature (T-c = 106 K at R = 0) and the critical current density (J(c) = 1.1 X 10(4) A/cm(2) at 77 K) were observed for the Ag-doped films (on Ag/MgO substrates), in comparison with those for the undoped films (on MgO substrates), The temperature dependence of the Ag diffusion coefficient in Bi-2212 films in the range 650-800 degrees C was described by the relation D = 2.2 X 10(-5) exp(-1.2/kT).