X-ray absorption spectroscopic study of new high-Tc superconducting intercalation compound of (HgX2)0.5Bi2Sr2CaCu2Oy(X=Br,I)

We have systematically performed x-ray absorption spectroscopic (XAS) studies on the new mercuric halide intercalated superconductors, (HgX ₂) _0.5Bi ₂Sr ₂CaCu ₂O _y with X equals Br and I, in order to investigate the electronic and crystal structure of these compounds. 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 angstrom for the HgBr ₂-intercalate and 2.65 angstrom for the HgI ₂-one. This is the first example of linear molecular salt of HgX ₂ stabilized in the solid lattice. According to the I L _I- and Br K-edge x-ray absorption near edge structure (XANES) spectroscopic studies, a small amount of electron transfer from the intercalant HgX ₂ to the host lattice could be observed upon intercalation, resulting in the negatively charged state of (HgX ₂) ^δ. The Cu K-edge EXAFS analysis reveals that the bond distance of Cu-O _axial is slightly shortened upon intercalation, reflecting the oxidation of (Cu-O) layer, which is well consistent with the I L _I- and Br K-edge XANES results.