In this study, TiO2 films with nanocrystal grains were synthesized by sol-gel route (Fig. 1). Tetrabutyltitanate (Ti (OC4H9)4) was used as the main raw reagent, and acetic acid (CH3COOH) and ethyl alcohol as solvents. Acetic acid was
Fig. 1 The preparation process of TiO2 film by sol gel route
mixed with polyvinylpyrolidone dissolved in ethyl alcohol and acetyl acetate and then Tetrabutyltitanate was added. The mixture was stirred vigorously at room temperature for 1 h to form TiO2 precursor.
Silicon wafers (coated with ITO (indium tin oxide)) were used as substrates for the deposition of TiO2 coatings.
Before deposition, the Si wafers were washed with ethyl alcohol, acetone and ammonium to eliminate adsorbed impurities and to form a stable film.
Sol-gel solution was dispersed on the substrates and then spin coated at 3000 rev./min for 60 s. One batch of samples were sintered at 300, 400, 500, 600, 700 and 800 °C for 2 h to study microstructure at different temperature. To study the changes in microstructure during the isothermal hold (700 °C), other samples were held for 1, 3, 6, 10, 30, 60, 100, 300, 600 min’s, and then allowed the furnace to cool. To study the sintering process in stages, samples were heated in atmospheric air with a heating rate of 3 °C/min in conventional furnace.
The crystallization process of TiO2 gel was studied with the aid of DSC/TG (German NETZSCH, STA449 F3), and XRD (powder diffractometer). The microstructure of the powders was examined with SEM (Hitachi SU-70). The grain size of TiO2 nanocrystals was calculated with image analysis IMAGE J and fractal dimension was calculated with FRACTAL ANALYSIS SYSTEM version 3.4.7.