Charge transfer-Tc relation in the superconducting intercalates IBi2Sr2CaCu2Oy

Two different kinds of stage-1 iodine intercalates of Bi2Sr2CaCu2Oy with dissimilar T-c have been prepared in order to understand the relationship between superconducting properties and electronic structures. According to the XRD analysis and the magnetic susceptibility measurements, it is found that, in spite of the same basal increments for both intercalates (Delta d = similar to 3.6 Angstrom), the iodine intercalate prepared in a vacuum-sealed tube exhibits a larger T-c depression (13 K) compared to the iodine intercalate synthesized in air (Delta T-c = 6 K). The origin of such different T-c shifts has been investigated by performing the systematic XANES/EXAFS analyses at the I L-1-, Cu K-, and Bi L-3-edges, where the charge transfer between host and guest is found to be strongly dependent on the reaction condition. From the BVS calculation based on the Cu K-edge EXAFS results, it is clarified that there is an excellent correlation between the amount of hole doping and T-c depression for both iodine intercalates. In this respect, we conclude that, regardless of lattice expansion along the c-axis, the T-c of Bi-based cuprate is wholly dependent on the hole concentration of the CuO2 layer. (C) 1998 Academic Press.