Role de la substitution du plomb au bismuth dans BiSrCaCuO et obtention de couches minces de résistance nulle au dessus de 100 K.

We point out a pronounced difference of percolation threshhold for the zero resistance of the 110 K superconducting phase between the lead-free and the lead substituted BiSrCaCuO thin films. This difference is accounted for by a major difference in the microstructure of the grains which has the effect that the lead-free case pertains to a 3-dimensional percolation scheme while the lead substituted case pertains to a 2-dimensional percolation one