Structural Phase Transition and Metallic Behavior in Misfit Layered (Bi,Pb)-Sr-Co-O System

Abstract

The crystal structure of Bi 2- x Pb x Sr 2 Co 2 O y has been investigated by X-ray diffraction and electron diffraction analyses. In contrast to what has previously been considered a Bi 2 Sr 2 CaCu 2 O 8 -type structure, we found that this material has a misfit layer structure: two subcells with different periodicities are alternately stacked. We have studied the x dependence of the crystal structure and found a discontinuous phase transition at x ≃0.2, where only Bi-Sr-O layers show a drastic change in lattice constants. Pb doping induces metallic behavior, but the effect of the structural phase transition is less clearly observed, which indicates that the electronic properties are mainly dominated by CoO 2 layers.