Structure of Compounds in the Sr_1–3x/2Ce_xTiO₃ Homologous Series

Four compositions in the Sr 1–3 x /2 Ce x TiO 3 homologous series, corresponding to x = 0.1333, 0.1667, 0.25, and 0.4, have been produced by conventional solid-state processing. The structure of these compounds was analyzed by X-ray, electron, and neutron diffraction. While no superlattice can be observed via X-ray diffraction, both electron and neutron diffraction show evidence of a noncubic supercell caused by antiphase tilting of oxygen octahedra. The most likely space group is R 3̅ c, corresponding to an a − a − a − tilt system, except for the composition x = 0.4, for which an even more complex superstructure is observed. The degree of tilt increases with increasing x .