Titanate Nanostructures Research Articles

Titanium oxide nanotubes, nanofibers and nanowires

A simple one-step hydrothermal reaction among TiO 2 powders and alkaline solution has been developed to synthesize low-dimensional titanate nanostructures. The morphologies of the obtained nanomaterials depend on the process parameters: the structure of raw material, the nature and concentration of alkaline solution, reaction temperature and time, which suggests that the nanostructure synthesis could be controllable. Trititanate nanotubes with the diameters of about 10 nm were synthesized via the hydrothermal reaction of TiO 2 crystals of either anatase or rutile phase and NaOH solution in the temperature range of 100–160 °C. Nanofibers with an interlinked structure were formed when amorphous TiO 2 or commercial TiOSO 4 was treated with NaOH at 100–160 °C. Pentatitanate nanoribbons with high aspect ratio were obtained by autoclaving of either crystalline or amorphous TiO 2 in NaOH solution at the temperature above 180 °C. Octatitanate nanowires with the diameters of 5–10 nm were prepared from TiO 2 particles treated with KOH solution. These nanostructures were analyzed by a range of methods including powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and infrared spectroscopy (IR).

PREPARATION OF TRANSPARENT, PARTIALLY-CRYSTALLIZED BATIO3 MONOLITHIC XEROGELS BY SOL-GEL PROCESSING

Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90°C) have been successfully synthesized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentration range of ≥1.0 mol/l with addition of water with a molar ratio of H2O/Ba ≥ 6.3. Transparent monolithic xerogels obtained from a precursor solution of 1.0 mol/l remained transparent even after firing at 500°C in oxygen, although the degree of their transparency was considerably decreased. Firing at temperatures above 500°C yielded translucent ceramics of BaTiO3, and ultimately, firing above 600°C resulted in normal opaque ceramic bodies. Those obtained from a more concentrated precursor solution of 1.2 mol/l were, on the other hand, still transparent after firing at 600°C in oxygen, and turned opaque at 700°C. The results demonstrate that the materials retained their transparency even after pyrolysis of organic compounds involving exothermic oxidation at temperatures in the range of 200 to 400°C. The densification behavior of transparent BaTiO3 monolithic xerogels obtained was found to be excellent; for example, those derived from a 1.0 mol/l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of ≈1 μm by firing at 1100°C for 2 h in oxygen.

XRD and raman study of nanostructured Lanthanum-modified lead titanate materials

Lanthanum-modified lead titanate (Pb1-xLaxTi1-x/4O3, X = 0.06 to 0.2) nanocrystalline powders were synthesized by stearic acid gel method. The structures of nanocrystals were characterized by powder X-ray diffraction (XRD), and the crystallographic parameters of samples were calculated. The results show that the tetragonality changes not only with La content but also with the grain size. The soft mode frequency decreases with an increase of La content and a decrease of grain size.