Structure of Al Defect in High-Temperature Superconductor, Al-Doped Sm-123: An Electron Density Study

Electron and X-ray diffraction studies on the new compound K2In12Se19 indicate disorder of one-dimensional units due to the existence of pronounced diffuse scattering. The diffuse intensities are torus-shaped, with the axes of the rings collinear to c*. Observations by high-resolution electron microscopy (HREM) confirm the presence of three-dimensionally ordered domains with variable size which are separated by antiphase boundaries. The sizes of the domains determine the shape of the diffuse intensity. Starting from the average structure it is possible to develop a model of domains which are three-dimensionally ordered. This model serves as a basis for simulated HREM images and electron diffraction patterns that show good agreement with experimental data. The diffuse scattering could be simulated qualitatively on the basis of a nonperiodic model of the real structure which consists of randomly packed rods.