Order and disorder in cerium-rich ceria-zirconia solid solutions revealed from reverse Monte Carlo analysis of neutron and x-ray total scattering

A reverse Monte Carlo analysis of neutron and x-ray total scattering data from two ceria-zirconia samples of composition Ce0.75Zr0.25O2 is performed to analyze the distribution of cations and to examine the possibility of oxide-ion disorder. For the first material, heated in air under moderate conditions (800?), the structure is a single-phase solid-solution with the statistical distribution of cations, but a local tetragonal symmetry is found, consistent with the different coordination preferences of Ce and Zr. For the second material, heated under H-2 at 1050? followed by reoxidation at 400 ?, the structure shows a considerable disorder, with evidence for oxygen interstitials (Frenkel-ion defects) and a non-statistical distribution of cations with significantly higher concentrations of like-like cation nearest neighbors, highlighting the existence of cation-rich nano-domains. The results highlight the dynamic nature of this solid-solution, with structural evolution upon thermal treatment, which is of relevance to understanding its stability under redox catalytic conditions in practical applications.