Structure of compounds in the Sr_1-3x/2Ce_xTiO ₃ homologous series

Four compositions in the Sr_1-3x/2Ce_xTiO₃ 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 R3̄c, 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.