A comparative XPS study of Bi2Sr2CaCu2O8 and Bi1.6Pb0.4Sr2CaCu2O8 compounds

The influence of Pb doping on the electronic structure of 2212 superconductor was investigated by XPS. The evolution of the core level spectra of the material components as a function of the sample treatment has shown that in situ heating at 450 degrees C allows to gain surface whose properties represent well those of the bulk. From detailed analysis of the high resolution XPS spectra we have deduced that the ions exist as Cu-(2+epsilon+), Sr2+, Ca2+, Pb2+ and Bi3+ and that each Sr and Ca ions in the lattice crystal have two occupation sites, Sr-O layer and Ca layer. The most remarkable influence of Pb concerned the enhancement of the thermal stability of the superconductor, proving the probable existence of an induced stronger interaction between Bi-O planes