Electron microscope studies of nano-domain structures in Ru-based magneto-superconductors: RuSr2Gd1.5Ce0.5Cu2O10-δ (Ru-1222) and RuSr2GdCu2O8 (Ru-1212)

Microstructures of the RuSr2Gd1.5Ce0.5Cu2O10-δ (Ru-1222) and RuSr2GdCu2O8 (Ru-1212) magneto-superconductors have been investigated by using selected-area electron diffraction, convergent-beam electron diffraction, dark-field electron microscopy and high-resolution electron microscopy at room temperature. Both Ru-1212 and Ru-1222 consist of nm-size domains stacked along the c direction, where the domains are formed by two types of superstructures due to ordering of rotated RuO6 octahedra about the c-axis. In Ru-1212, both primitive-and body-centered tetragonal superstructures (the possible space groups: P4/mbm and I4/mcm) are derived to form the corresponding nm-domains. It is of great interest that Ru-1212 consists of domains of two crystallographically different superstructures, while the similar domains observed in Ru-1222 have crystallographically identical superstructure with an orthorhombic symmetry (possible space group: Aeam), related by 90 degree rotation around the c-axis (Yokosawa et al., 2003, submitted for publication)