Intracrystalline Structure of Molecular Mercury Halide Intercalated in High-Tc Superconducting Lattice of Bi2Sr2CaCu2Oy

Abstract

X-ray absorption spectroscopic studies have been systematically carried out for the new high-Tc superconducting intercalation compounds, (HgX2)0.5Bi2Sr2CaCu2Oy (X = Br and I), with a hybridized crystal lattice consisting of superconducting layer and insulating one. From the Hg LIII-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 Å for the HgBr2 intercalate and 2.65 Å for the HgI2 one, respectively. These are cross-confirmed not only by micro-Raman studies but also by one-dimensional electron density mapping based on (00l) X-ray reflections, which is well consistent with the EXAFS fitting results. The present I LI- and Br K-edge XANES results indicate a partial electron transfer from the host lattice of Bi2Sr2CaCu2Oy to the intercalant HgX2 layer with the partial oxidations of Bi2O2 and CuO2 layers. And the latter was also observed clearly from the Bi LIII-edge XANES and Cu K-edge EXAFS analyses, which are in good agreement with the I LI- and Br K-edge XANES results. It is, therefore, concluded that the charge transfer between host and guest is mainly responsible for the Tc evolution upon intercalation, and the Tc of this compound is surely related to the variation of hole concentration rather than electronic coupling along the c-axis.