X-Ray Photoelectron Spectroscopy Studies of 7 K-Phase Bi-System Single Crystals

The Bi-system single crystals with c -axis unit cell length of ∼24 Å, i.e., Bi-Sr-Cu-O (BSCO), Bi-Pb-Sr-Cu-O (BPSCO), Bi-Sr-Ca-Cu-O (BSCCO), and Bi-Pb-Sr-Ca-Cu-O (BPSCCO) single crystals, were prepared using the starting materials of various compositions by the self-flux method. X-ray photoelectron spectroscopy (XPS) measurements from the air-cleaved surfaces of the single crystals were carried out. From the results of the surface composition analyses, we found that Pb occupied a part of the Bi site in the BPSCO single crystal and Ca occupied a part of the Sr site in the BSCCO single crystal. The chemical bond natures of Sr, Cu and O in the BSCO crystal seem to be changed by doping with Pb and/or Ca.