Heterostructured Bi-Based Cuprate High-Tc Superconductors with Unusually Coordinated Metal Halides

Abstract

Attempts have been made to prepare various high-Tc superconducting intercalation compounds, M–X–Bi2Sr2Can−1CunO2n+4+δ (M=metal; X=halogen; n=1, 2, and 3), with the synthetic strategy of hard–soft–acid–base interaction. The chimie douce route such as vapor transport and ionic diffusion is found to be effective in intercalating soft Lewis acidic guest species (I−3, AgxIx−ww, HgIδ−2, HgBrδ−2, and AuIδ−3) into the Lewis basic Bi2Sr2Can−1CunO2n+4+δ lattice. According to the X-ray diffraction and magnetic property measurements on these intercalates, it becomes clear that the basal increment upon intercalation (3.25–7.35 Å) is governed by the interlayer geometry of the intercalant, while the accompanying Tc change depends on the charge transfer between host and guest. The extended X-ray absorption fine structure and Raman studies reveal that mercuric halides are intercalated as linear molecules as in vapor state, while silver iodide forms a two-dimensionally extended ionic-conducting channel. In the case of new gold iodide intercalate, unique trigonal planar AuI3 species is identified as the first example of an isolated gold iodide molecule.