Chemical bonding between host and guest in the (HgBr2)0.5Bi2Sr1.5−xLaxCa1.5Cu2Oy (x=0.0, 0.2, and 0.4) superconducting-insulating nanocomposite system

Abstract

X-ray-absorption spectroscopic studies have been systematically carried out for the La-substituted Bi2Sr1.5−xLaxCa1.5Cu2Oy (x=0.0, 0.2, and 0.4) compounds and their HgBr2 intercalates in order to characterize the variation of the chemical bonding nature of host and guest upon substitution and intercalation reactions. According to the Cu K-edge x-ray-absorption near-edge structure-extended x-ray-absorption fine-structure analyses, it is found that the oxidation state of the CuO2 layers is reduced by substituting the Sr+II ion with La+III, while it is enhanced by the intercalation of HgBr2. Such findings provide clear evidence of the main role of charge transfer in determining the Tc of the intercalate. The chemical bonding between host lattice and intercalant layer has also been investigated by performing the Br K-edge and Hg LIII-edge x-ray-absorption spectroscopic analyses, indicating that a small fraction of electrons are transferred from host to guest and that the bond strength of Hg-Br as well as of Br-Bi is changed as the La-substitution rate increases. These results underline that the local substitution of La+III ions into the SrO plane gives rise to the overall changes for all the chemical bonds in these superconducting lattices and clarify that the competing bond model can be effectively applied to the chemically substituted superconducting oxides.

Source-reported materials — not catalogue approval

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