Crystal Structure and Microstructure of Some La_2/₃_-<i>_x</i>Li₃<i>_x</i>TiO₃ Oxides:  An Example of the Complementary Use of Electron Diffraction and Microscopy and Synchrotron X-ray Diffraction To Study Complex Materials

Three representative oxides of the La(2/3)(-)(x)()Li(3)(x)()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 ( radical 2a(p) x radical 2a(p) x 2a(p)) as a consequence of the tilting of the TiO(6) 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.