An environmentally friendly aqueous sol-gel process has been developed to fabricate thin films of indium tin oxide (ITO). A stable sol was prepared from indium nitrate and tin acetate precursors together with acetic acid and ethylene glycol. The sol transformed into an amorphous gel during heating, which decomposed and crystallized further to nano-crystalline ITO at $300 C. The nanocrystalline ITO powders prepared from the precursor gel were homogeneous and single phase with particle sizes around 15 nm. The aqueous sol was applied for spin coating of ITO films on glass substrates. The deposited thin films were homogeneous and continuous with no cracks or pin-holes and exhibited very good and reproducible optical transparency and electrical conductivity, with a specific resistance of 4.59 Â 10 À3 U cm, thereby demonstrating the potential of this Pechini related sol-gel process. Experiments to determine the robustness of the process with respect to the concentration of the precursors and substitution of the organic components with other alcohols or acids were also performed, and some important aspects of the chemistry of the sol-gel process are addressed.

Novel bur-like hierarchical nanostructures of PbTiO3 were prepared by hydrothermal synthesis. Surfactants containing phenyl-sulfonic groups resulted in self-assembly of nanocrystals. In absence of the surfactant, monodisperse PbTiO3 microspheres were formed. The microspheres were 1−5 μm in diameter, and consisted of ∼20 nm tetragonal PbTiO3 crystals. The microspheres were formed by primary nucleation of PbTiO3 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 PbTiO3 nanocrystals into microspheres occurs. PbTiO3 mesocrystals are formed at the surface of the microspheres by self-assembly of cube-shaped or facetted PbTiO3 nanocrystals, and the mesocrystals ripen and grow further into nanorods.

A molten salt synthesis route, previously reported to yield BaTiO3, PbTiO3, and Na2Ti6O13 nanorods, has been re-examined to elucidate the role of volatile chlorides. A precursor mixture containing barium (or lead) and titanium was annealed in the presence of NaCl at 760 or 820 degrees C. The main products were respectively isometric nanocrystalline BaTiO3 and PbTiO3. Nanorods were also detected, but electron diffraction revealed that the composition of the nanorods was respectively BaTi2O5/BaTi5O11 and Na2Ti6O13 for the two different systems, in contradiction to the previous studies. It was shown that NaCl reacted with BaO (PbO) resulting in loss of volatile BaCl2 (PbCl2) and formation and preferential growth of titanium oxide-rich nanorods instead of the target phase BaTiO3 (or PbTiO3). The molten salt synthesis route may therefore not necessarily yield nanorods of the target ternary oxide as reported previously. In addition, the importance of NaCl(g) for the growth of nanorods below the melting point of NaCl was demonstrated in a special experimental setup, where NaCl and the precursors were physically separated.

Here we report on molten salt synthesis of four different compounds in the K 2 O-Na 2 O-Nb 2 O 5 system. The three compounds K 4 Nb 6 O 17 , K 2 Nb 4 O 11 and KNb 3 O 8 , with non-cubic crystal structures, were prepared as single crystalline particles with large aspect ratios. K 4 Nb 6 O 17 was prepared with a platelike morphology, K 2 Nb 4 O 11 a fibre-like and finally KNb 3 O 8 had a plate like morphology. K x Na 1Àx NbO 3 , with a cubic perovskite crystal structure at the synthesis conditions, was only obtained as cube-shaped crystals, which became larger with increasing synthesis temperature. A systematic study of the influence of the processing conditions on the morphology of the product compounds was conducted. The study demonstrated that the morphology of the product phase was controlled by the crystal structure and the connectivity of the NbO 6 -octahedra of the crystal structures. Finally, the crystal structure of K 2 Nb 4 O 11 was determined to be a tungsten bronze type structure with space group P4/mbm.

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