On the crystal structures of La2Ti2O7 and La5Ti5O17: High-resolution electron microscopy

The structure of La5Ti5O17 has been examined by high-resolution transmission electron microscopy combined with powder X-ray and thermogravimetric analysis. It comprises five [TiO6] octahedra-thick layers isomorphous with {1 0 0} slabs of the LaTiO3 orthorhombic perovskite structure, bounded by crystallographic shear parallel with the perovskite [0 0 1] direction. La atoms occupy the distorted perovskitic A sites. The structure is derived from the homologous La2Ti2O7 by elimination of 135 of the oxygens from this four-octahedra-thick layered structure. Both compounds are members of an homologous series based on variation in the anion to cation ratio.