Assignment of fluorine sites in (Tl0.5Pb0.5)Sr1.6Ba0.4Ca2Cu3Oy/F-x

Fluorine 1s and Cu 2p core level binding energies of (T1(0.5)Pb(0.5))Sr1.6B a0.4Ca2Cu3Oy/F-x for nominal x = 0.0, 1.0, 2.2 and 3.0 were measured by X-r ay photoelectron spectroscopy (XPS) in order to identify the F site in the overdoped superconductors. Detailed data analysis indicate that about two t hirds of the incorporated F replace O in Cu-O planes of the T1-1223 structu re. Most of the remaining one third of F replaces O in the Ba/Sr-O planes a nd a small amount of F substitutes for O in the T1/Pb-O planes of T1-1223 s tructure. Cu 2p(3/2) binding energy was found to be decreasing with increas ing x. This indicates that the valency of Cu in T1-1223/F-x decreases as x increases. The reduction of charge carriers in the overdoped high temperatu re superconductors is discussed in terms of anion substitution. (C) 2000 El sevier Science B.V. All rights reserved.