A COMPARATIVE X-RAY PHOTOEMISSION-STUDY OF BI2SR2CACU2O8+DELTA AND BI1.6PB0.4SR2CACU2O8+DELTA'

The influence of Pb doping on the electronic structure of Bi2Sr2CaCu2O 8+delta superconductor was investigated by X-ray photoelectron spectro scopy. A surface preparation procedure consisting of an annealing in U HV at 450 degrees 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 sh own that the core-level spectra of Ols, Cu2p, Sr3d, Ca2p, Bi4f and Pb4 f are insensitive to the presence of Pb. The ratio of the two occupati on 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 enh ancement of the thermal stability of the superconductor. This stabilit y enhancement is attributed to the existence of a chemical bonding bet ween the Pb-substituted Bi-O planes.