Geometrical Relations of Various Modulated Structures in Bi-Sr-Ca-Cu-O Superconductors and Related Compounds

Abstract

Geometrical relations of the three types of modulated structures in Bi-based superconductors are discussed. The constituent blocks of width B s , wavelength of wavy perovskite and BiO layers, are packed in various ways to form various structures. Body-centered orthorhombic structures in Bi-Sr-Ca-Cu-O superconductors are derived by B s /2 displacements between upper and lower blocks, whereas the B-centered monoclinic structure in the Bi-Sr-Cu-O one is derived by nearly B s /4 displacement. Another orthorhombic structure, recently found in Bi-Pb-Sr-Ca-Cu-O superconductor, is possibly due to the simple arrangements of blocks with no mutual displacement.