Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present a local disorder within the perovskite unit cell, associated with the existence of a polar ordering. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubilities in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 32 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 oC. We report here on the synthesis and self-assembly of aggregate-free single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them.
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