Pyrolysis pathway of sol-gel derived organic/inorganic hybrid nanocomposites

The thermal alteration of hybrid polydimethylsiloxane–titania nanometer sized composites (nanocomposites) has been studied up to 1600 °C to determine the changes of the silicon oxycarbide phase as a function of temperature and titania content. The samples were prepared by the sol–gel method starting from molecular precursors, diethoxydimethylsilane and titanium isopropoxide. The starting xerogels were treated under argon atmosphere and their phase changes were observed by thermal analyses, infrared spectroscopy, and X-ray diffraction. Between 500 and 800 °C the polymer-to-ceramic conversion takes place for all samples with the formation of differing oxycarbide phases, whose structures depend on the titania content. At 1000 °C two main phases are present, which we describe as silicon oxycarbide and titanium oxycarbide phases. Their change with increasing temperature has been followed using quantitative X-ray diffraction analyses, using a modified Rietveld method. Under the assumption that a crystalline phase with periodic order comparable with the unit cell lengths could fit an amorphous phase, a simplified silica structure has been used for the refinement of the silicon-derived phase. This novel approach has been used here to describe the structural changes of the amorphous silicon oxycarbide phase during the pyrolysis process and as a function of Ti content by measuring the changes of the cell parameter a.