Compositional Relationship between Superconducting “Raveau” Phase and Non-Superconducting “Collapsed-221” Phase

Abstract

A large number of specimens were synthesized in a wide range of cations for the Sr and Bi-sites in the Sr₅Bi₆Cu₃O₁₇ (563; R-phase) and Sr₇Bi₆Cu₄O₂₀ (764; C-phase) compositions. Superconductivity (T_c-10K) in R-phase solid solution was found only including PbO, which formulated as Sr₇(Bi₆Pb_x) Cu₄O_20+x (1<x<2). It showed that Pb addition is essential for the formation of a single R-phase superconductor. In addition, a new C-phase compound composition with (Sr₅Ba)Bi₆Cu₃O₁₈ was also found. The crystal chemical criteria favorable for the formation of R- and C-phase compounds were clarified by using the composition ratio of (A) Sr/Bi. It is represented as follows; R-phase<1.0<C-phase.