Comparison study on the size and phase control of nanocrystalline TiO2 in three Ti-Si oxide structures

Three types of Ti-Si binary oxides have been prepared by sol-gel processes. The effects of SiO2 addition and annealing temperature on the grain size, phase transition, dispersion, and microstructure of nanocrystalline (nc) TiO2 anatase in the three Ti-Si oxide structures have been comparatively investigated by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). The grain growth and anatase-rutile transformation (ART) of ncTiO(2) were found to depend not only on the SiO2 content and annealing temperature, but also on the composite structure. Both the grain growth and the ART of ncTiO(2) proved to be significantly inhibited with increasing SiO2 content for all of the Ti-Si samples, but the structure of intimately mixed Ti-Si binary oxide showed the best inhibiting ability under high-temperature annealing. This result might be attributed to variations in the large lattice strains in ncTiO(2), which were mainly induced by the substitution of Ti4+ by Si4+. Plausible mechanisms for the grain growth and ART of ncTiO(2) are proposed. To inhibit the grain growth of ncTiO(2), the addition of 10 and 30 mol% SiO2 proved to be optimal for Ti-Si samples annealed at 773 K and 1273 K, respectively.