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-1CunO 2n+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-w w, HgIδ- 2, HgBrδ- 2, and AuIδ- 3) into the Lewis basic Bi2Sr2Can-1CunO 2n+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. © 1999 Academic Press.