A comparative X-ray photoemission study of Bi2Sr2CaCu2O8+δ and Bi1.6Pb0.4Sr2CaCu2O8+δ′

The influence of Pb doping on the electronic structure of Bi2Sr2CaCu2O8+δ superconductor was investigated by X-ray photoelectron spectroscopy. A surface preparation procedure consisting of an annealing in UHV at 450°C was used to obtain surfaces representative of the superconductor intrinsic bulk properties. A careful comparison of the XPS characteristics between Pb-doped and undoped 2212 materials has shown that the core-level spectra of O1s, Cu2p, Sr3d, Ca2p, Bi4f and Pb4f are insensitive to the presence of Pb. The ratio of the two occupation sites of Sr and Ca in the crystal lattice is strictly unchanged by doping. The most remarkable influence of Pb is the slight shift of 0.1 eV towards low binding energy of the valence band spectra and the enhancement of the thermal stability of the superconductor. This stability enhancement is attributed to the existence of a chemical bonding between the Pb-substituted BiO planes.