Microdomain Structure in YBa2(Cu1-xFex)3O7-y Observed by Electron Microscopy

Abstract
The Fe-doped high-Tc superconducting phase YBa2(Cu1-xFex)3O7-y has been investigated by electron microscopy. The sample with x=0.04 shows a microdomain structure composed of ordered domains with sizes of about 5 nm, while an ordinary striped twin pattern is observed for x=0.02. The impurity-induced orthorhombic to tetragonal transition observed by X-ray diffraction measurements can be explained as resulting from the specific structure: Each domain possesses the orthorhombic structure including 1-D Cu-O chains ordered along the [100] or [010] direction, and two orientation variants are mixed coherently leading to an "averaged" tetragonal symmetry as observed by diffraction methods.