Structural characterization of the sol-gel oxide powders from the ZnO-TiO2-SiO2 system

This work is a study that deals with the synthesis by the sol-gel method and the structural characterization of the oxide powders belonging to the ternary system ZnO-TiO2-SiO2 (ZTS). The sol-gel synthesis starts from inorganic precursors, which have been processed under the variation of different technological parameters. We have investigated the dependence of the gelling time on pH and on the temperature of synthesis as well as on water and ammonia amounts. In the case of ZTS samples, the shortest gelling duration appears for low pH values when ZnO content is increased and at small ammonia concentrations when the ZnO content is decreased, respectively. On the contrary, ZTS samples containing high amounts of TiO2 provide evidence of a short gelling time for high pH and large ammonia amounts. Xray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy provided structural information on these ternary oxide powders. These analyses revealed that relative high amounts of ZnO yields in a change from octahedral [ZnO6] units to tetrahedral [ZnO4] units in the powder structure. Optical phonons specific for SiO2 and TiO2 in both octahedral and tetrahedral groups are shown. High thermal and chemical stability was put in evidence by differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) in the 20-1000 degrees C temperature range. (c) 2007 Elsevier Ltd. All rights reserved.