Self-Assembled Growth of PbTiO₃ Nanoparticles into Microspheres and Bur-like Structures

Novel bur-like hierarchical nanostructures of PbTiO 3 were prepared by hydrothermal synthesis. Surfactants containing phenyl-sulfonic groups resulted in self-assembly of nanocrystals. In absence of the surfactant, monodisperse PbTiO 3 microspheres were formed. The microspheres were 1−5 μm in diameter, and consisted of ∼20 nm tetragonal PbTiO 3 crystals. The microspheres were formed by primary nucleation of PbTiO 3 nanocrystals followed by aggregation into microspheres. The hierarchical bur-like nanostructures exhibit a unique geometry consisting of a microsphere core with an outer shell of nanorods. The nanorods, which grow along the [001] direction, were ∼50−100 nm in diameter and from several hundreds of nanometers up to 2 μm in length. A mechanism for the growth of the bur-like nanostructures was proposed. First, agglomeration of PbTiO 3 nanocrystals into microspheres occurs. PbTiO 3 mesocrystals are formed at the surface of the microspheres by self-assembly of cube-shaped or facetted PbTiO 3 nanocrystals, and the mesocrystals ripen and grow further into nanorods.