Crystal Structure and Microstructure of Some La_(2/3-x)Li_(3x)TiO_3 Oxides: An Example of the Complementary Use of Electron Diffraction and Microscopy and Synchrotron X-ray Diffraction To Study Complex Materials

摘要

Three representative oxides of the La_(2/3-x)Li_(3x)TiO_3 system have been studied by selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), and powder synchrotron X-ray diffraction. HRTEM showed that the materials have a complex microstructure. The SAED and HRTEM results have allowed us to propose a model to refine the crystal structure of these oxides that also accounts for their microstructure. The materials have a perovskite-related structure with a diagonal unit cell (√2a_p × √2a_p × 2a_p) as a consequence of the tilting of the TiO6 octahedra. Ordering of lanthanum and lithium ions and vacancies along the 2a_p-axis, as well as displacements of titanium ions from the center of the octahedra, have been determined. The size and shape of the domains have been obtained from the synchrotron X-ray diffraction data; in addition, other extended defects such as strains and compositional fluctuations have been detected.