Search

Abstract: A new aqueous solution–gel precursor based on water soluble glycolato(-peroxo)–Ti(IV) complexes is developed for the preparation of TiO2 films. With regard to the decomposition of complexes towards oxide formation, it is important to gain insight in the chemical transformations inside the precursor during thermal treatment. Therefore, the thermo-oxidative decomposition pathway of a gel obtained by slow evaporation of the precursor solution is described based on hyphenated thermogravimetric analysis with Fourier transform infrared spectroscopy (TGA–FTIR) and mass spectrometry (TGA–MS). Pure glycolic acid is used as a reference system for this study. By varying the molar glycolic acid to Ti(IV) ratio, the thermal decomposition of the gel can be drastically shortened and the profile''s course changed. Gel structure and chemical changes in the gel upon heating are also studied by means of off-line FTIR. A unidentate coordination of the titanium(IV) ion by the carboxylate group of the glycolato ligands and the involvement of the hydroxyl group is confirmed. Phase formation at certain points in the thermal decomposition is studied by X-ray diffraction and Raman spectroscopy. Finally, it is proven that the new precursor is a valuable candidate for the deposition of low carbon containing solution–gel films which can ultimately be converted into smooth and uniform TiO2 films. [Copyright &y& Elsevier]

The factors influencing crystallization of layered-perovskite lanthanum substituted bismuth titanate, starting from an aqueous metal-chelate precursor-gel, were identified by means of statistically designed experiments. To ensure experimental economy and efficiency in spite of the large number of factors possibly affecting the phase purity, a fractional factorial design was chosen. The calcination atmosphere turned out to be the most important to avoid the formation of the Sillenite secondary phase, Bi12TiO20. In order to study its impact on phase purity thoroughly an extensive number of ambient compositions were tested. These tests showed that dry air is the optimal composition. Precursor stoichiometry and gas flow rate during heat treatment also significantly influenced the formation of Bi12TiO20. Furthermore, the precursor stoichiometry and cooling rate as well as the calcination atmosphere and crystallization time turned out to interact. [Copyright &y& Elsevier]