Radiation Chemistry Provides Nanoscopic Insights into the Role of Intermediate Phases in CeO(2) Mesocrystal Formation

The role of intermediate phases in CeO(2) mesocrystal formation from aqueous Ce(III) solutions subjected to γ‐radiation was studied. Radiolytically formed hydroxyl radicals convert soluble Ce(III) into less soluble Ce(IV). Transmission electron microscopy (TEM) and X‐ray diffraction studies of samples from different stages of the process allowed the identification of several stages in CeO(2) mesocrystal evolution following the oxidation to Ce(IV): (1) formation of hydrated Ce(IV) hydroxides, serving as intermediates in the liquid‐to‐solid phase transformation; (2) CeO(2) primary particle growth inside the intermediate phase; (3) alignment of the primary particles into “pre‐mesocrystals” and subsequently to mesocrystals, guided by confinement of the amorphous intermediate phase and accompanied by the formation of “mineral bridges”. Further alignment of the obtained mesocrystals into supracrystals occurs upon slow drying, making it possible to form complex hierarchical architectures.