Shape-controlled monocrystalline ferroelectric barium titanate nanostructures: From nanotubes and nanowires to ordered nanostructures

We report for the first time on the controlled hydrothermal synthesis of barium titanate nanostructures using Na₂Ti₃O₇ nanotubes and nanowires as synthetic precursors. A variety of nanostructured BaTiO₃ have been prepared, exhibiting either simple shapes of nanowires, nanosheets, nanocubes, and hexagonal nanoparticles or ordered architectures of coral-like nanostructures of assembled nanorods, starfish-like nanostructures, and sword-like nanostructures. The shapes of the various BaTiO₃ products are found to be dependent on the concentration of Ba(OH)₂, the temperature, and the nature of the precursors. The synthesis route exploits the differences in the hydrothermal stability of the Na₂Ti₃O₇ nanotubes and nanowires and the temperaturedependent crystal structure of barium titanate. Various nanoblocks, including nanosheets and nanorods formed from the Na₂Ti ₃O₇ nanotubes and nanowires, respectively, grow and assemble to form the ordered BaTiO₃ nanostructures. This represents a new approach that is capable of assembling ordered perovskite nanostructures using relatively large nanoblocks formed from layered alkali-metal titanates. The process offers more flexibility than those using inorganic titanium salts or organometallic titanium compounds, which commonly leads to the formation of only BaTiO₃ nanoparticles.