CHARGE TRANSFER-T-C RELATION IN THE SUPERCONDUCTING INTERCALATES IBI2SR2CACU2OY

Two different kinds of stage-1 iodine intercalates of Bi2Sr2CaCu2Oy wi th dissimilar T-c have been prepared in order to understand the relati onship between superconducting properties and electronic structures. A ccording to the XRD analysis and the magnetic susceptibility measureme nts, it is found that, in spite of the same basal increments for both intercalates (Delta d = similar to 3.6 Angstrom), the iodine intercala te 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 dopi ng and T-c depression for both iodine intercalates. In this respect, w e 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.