Bi,M Sr2(R,Ce)nCu2Oy (M=Cu, Cd; R=Nd,Gd; n=1,2, and 3): A Family ofSuperconductors That Exhibit Superconductivity at Tc approximately 20 K for n=3 with Double Fluorite Blocks and Monolayer (Bi,M)O Sheets

摘要

The authors report the discovery of a family of Bi-based superconductors,(Bi,M)Sr2(R,Ce)nCu2Oy(n=1,2,3), one member of which (n=3) exhibits bulk superconductivity at T(sub c)=20 K. The crystal structures of these materials are similar to those of (Ti, Cu)Sr2(R,Ce)nCu2Oy, but the Tl-based 1:2:3:2 phase (n=3) shows semiconductive behavior. These compounds contain Cu perovskitelike units and zero, one, and two fluorite units, respectively. They are sandwiched between monolayer Bi-O sheets, but while the Cu perovskitelike units are separated by bilayer Bi-O sheets in Bi2Sr2CanCu(n+1)Oy (n=0,1, and 2), it is found that superconducting transition temperatures decrease sharply when the spacing between CuO2 planes increases. It provides evidence of the effect of the coupling between successive Cu perovskite units and of the stacking pattern of adjacent Cu sheets on the superconductivity.