Incommensurate superlattice and 90° twist boundaries in the superconducting phase of Bi-Sr-Ca-Cu-O

Abstract

We have observed an incommensurate superlattice structure in the Bi-Sr-Ca-Cu-O system using electron diffraction. The wave vector of the superlattice, $q=(0,\frac{1}{4.7},1)$, has an incommensurate component along the $b$ axis and a commensurate component along the $c$ axis. Twist boundaries perpendicular to the $c$ axis, across which the crystallographic $a$ and $b$ axes are rotated 90\ifmmode^\circ\else\textdegree\fi{}, are commonly observed in this system.