XPS studies of high-Tc superconducting Bi2Sr2Ca(Cu1-yFey)2Ox single crystals

Fe-substituted Bi2S2Ca(Cu1-yFey)(2)O-x single crystals have been studied by X-ray photoelectron spectroscopy (XPS) to determine the changes of oxidation states of their constitutes as well as the electronic structure of the valence band of the system. The core level lines of Bi exhibit two main components, which indicates either inequivalent sites or the presence of different oxidation states. The second component shows a systematic increase with Fe-substitution. The Sr Lines also exhibit two components in which the lower binding energy component decreases with the dopant content. No significant changes in CuO2 bilayers and Ca-O layer were observed. The results suggest a dramatic charge transfer between the Bi-O and Sr-O layers which compensates the increase of positive charge near the CuO2 planes induced by Fe-substitution for Cu, and the impurity scattering of the dopants in the conduction band is one of the key factors for the T-c suppression. (C) 1999 Elsevier Science B.V. All rights reserved.