X-ray and neutron diffraction study of intermediate phases in nonstoichiometric cerium dioxide

Powder samples of reduced ceria, CeO/sub 2 - x/, of known compositions in the range 0 less than x less than 0.3 have been examined by x-ray and neutron diffraction techniques in order to determine which intermediate phases belonging to the homologous series Ce/sub n/O/sub 2n - 2/ (with n = integer) truly exist. Through the appearance of superlattice lines in the neutron diffraction patterns, the existence of four distinct phases, corresponding to n = 7, 9, 10, and 11 was established. Aside from the phase Ce7O12, the structures of these phases cannot be accounted for with rhombohedral cells based on (111) vacancy strings, but indicate lower (monoclinic or triclinic) symmetry. The structure of Ce9O16 and Ce10O18 do not agree with structures proposed for the analogous Pr/sub n/O/sub 2n - 2/ compounds