X-Ray Absorption Spectroscopic Study of New High-T_c Superconducting Intercalation Compound of (HgX₂)_0,5Bi₂Sr₂CaCu₂O_y (X = Br, I)

Abstract
We have systematically performed X-ray absorption spectroscopic (XAS) studies on the new mercuric halide intercalated superconductors, (HgX₂)_0.5Bi₂Sr₂CaCu₂O_y with X = Br and I, in order to investigate the electronic and crystal structures of these compounds. According to the I L_I- and Br K-edge X-ray absorption near edge structure (XANES) spectroscopic analyses, it is found that a small amount of electron is transferred from the intercalant HgX₂ to the host lattice, resulting in the negatively charged state of (HgX₂)^δ-. The Cu K-edge extended X-ray absorption fine structure (EXAFS) analysis reveals that the bond distance of (Cu-O_axial) is slightly shortened upon intercalation, reflecting the oxidation of CuO₂ layer, which is well consistent with the I L_I- and Br K-edge XANES results. On the other hand, the present Hg L_III- edge EXAFS results indicate that the mercury is coordinated with two bromide or iodide ligands with bond length of 2.46 Å for the HgBr₂-intercalate and 2.65 Å for the HgI₂-one, respectively. This is the first example of linear molecular salt of HgX₂ stabilized in the solid lattice.