Colloidal Synthesis of Monodisperse High-Entropy Rare-Earth Oxide Nanoplatelets

High-entropy rare-earth oxides (HE-REOs) offer a broad compositional space for tuning defect chemistry, lattice distortion, and local atomic environments, yet their controlled synthesis as monodisperse and structurally well-defined nanostructures remains challenging. Here, we report a colloidal approach for the synthesis of solution-dispersible, single-crystalline HE-REO nanoplatelets. The ultrathin two-dimensional nanoplatelets adopt a trigonal REO lattice that supports homogeneous multication incorporation across ternary to denary HE-REO compositions, and a simultaneous multication nucleation and growth pathway is demonstrated. Atomic-resolution imaging, combined with binary-type intensity classification, enables assessment of local chemical ordering, and increasing configurational entropy drives the system from a nearly random local structure toward a heteroelement-dominated short-range ordered state. High-entropy design further facilitates the incorporation of chemically dissimilar nonrare-earth cations, expanding the accessible miscibility window of REO nanostructures. Our work establishes colloidal synthesis as both a versatile route to monodisperse high-entropy oxide nanostructures and a model platform for probing and understanding entropy-governed behavior and functionality in high-entropy materials.