INTRACRYSTALLINE STRUCTURE OF MOLECULAR MERCURY HALIDE INTERCALATED IN HIGH-T-C SUPERCONDUCTING LATTICE OF BI2SR2CACU2OY

X-ray absorption spectroscopic studies have been systematically carrie d out for the new high-T-c superconducting intercalation compounds, (H gX(2))(0.5)Bi2Sr2CaCU2Oy (X = Br and I), with a hybridized crystal lat tice consisting of superconducting layer and insulating one. From the Hg L(III)-edge EXAFS analysis, it is found for the first time that the intercalated mercuric halide is stabilized as a linear molecule with the bond distance (Hg-X) of 2.46 Angstrom for the HgBr2 intercalate an d 2.65 Angstrom for the HgI2 one, respectively. These are cross-confir med not only by micro-Raman studies but also by one-dimensional electr on density mapping based on (001) X-ray reflections, which is well con sistent with the EXAFS fitting results. The present I L(I)- and Br K-e dge XANES results indicate a partial electron transfer from the host l attice of Bi2Sr2CaCu2Oy to the intercalant HgX(2) layer with the parti al oxidations of Bi2O2 and CuO2 layers. And the latter was also observ ed clearly from the Bi L(III)-edge XANES and Cu K-edge EXAFS analyses, which are in good agreement with the I L(I-) and Br K-edge XANES resu lts. It is, therefore, concluded that the charge transfer between host and guest is mainly responsible for the T-c evolution upon intercalat ion, and the T-c of this compound is surely related to the variation o f hole concentration rather than electronic coupling along the c-axis.