Formation of Bi4Ti3O12 One-Dimensional Structures by Solid-State Reactive Diffusion. From Core−Shell Templates to Nanorods and Nanotubes
Résumé
One-dimensional nanostructures are usually fabricated using liquid-phase chemical methods or growth from the vapor phase. A different approach is proposed in this investigation. Using two different kinds of reactive templates with core−shell structure obtained using colloidal chemistry methods, we fabricated for the first time Bi4Ti3O12 nanorods and nanotubes by means of solid-state reactions. The intimate contact of the parent compounds in the core−shell template resulted in low reaction temperatures (500−600 °C), overcoming the morphological instability problem of one-dimensional (1D) templates. As the formation of bismuth titanate is dominated by the coupled ambipolar diffusion of Bi3+ and O2− ions through the titanate layer, the final morphology, nanorod or nanotube, is determined by the relative arrangement of the parent compounds in the core−shell template. When the bismuth precursor is located in the shell region and the core is a single-crystal TiO2 nanowire, formation of a single-crystal Bi4Ti3O12 nanorod occurs by a topochemical reaction. Opposite, when the shell corresponds to nanocrystalline TiO2 and the core to the bismuth precursor, the reaction leads to a porous nanorod or a nanotube depending on the template thickness. The development of the central cavity is ascribed to the coalescence of Kirkendall porosity and the effect of mechanical stresses accumulated during the reaction. The present results indicate that a careful control of the solid-state reactions at the nanoscale can be achieved by means of reactive templates with core−shell structure thus providing an effective tool for the design and the large-scale fabrication of a variety of nano-objects with different dimensionalities.