We have systematically performed x-ray absorption spectroscopic (XAS) studies on the new mercuric halide intercalated superconductors, (HgX2)0.5Bi2Sr2CaCu2Oy with X equals Br and I, in order to investigate the electronic and crystal structure of these compounds. The present Hg LIII-edge EXAFS results indicate that the mercury is coordinated with two bromide or iodide ligands with bond length of 2.46 angstrom for the HgBr2-intercalate and 2.65 angstrom for the HgI2-one. This is the first example of linear molecular salt of HgX2 stabilized in the solid lattice. According to the I LI- and Br K-edge x-ray absorption near edge structure (XANES) spectroscopic studies, a small amount of electron transfer from the intercalant HgX2 to the host lattice could be observed upon intercalation, resulting in the negatively charged state of (HgX2)(delta -). The Cu K-edge EXAFS analysis reveals that the bond distance of Cu-Oaxial is slightly shortened upon intercalation, reflecting the oxidation of (Cu-O) layer, which is well consistent with the I LI- and Br K-edge XANES results.
|