Water-assisted crystallization and densification of sol–gel-derived TiO2 films during low-temperature heating

Abstract

ABSTRACT The crystallization and densification behavior of TiO2 films during heating at below 400°C was studied for sol–gel coatings and the effect of the H2O content in the precursor solutions on the nucleation and crystal growth of anatase at such relatively low temperature was discussed. TiO2 gel films were prepared from Ti(OC3H7 i )4:HNO3:H2O:C2H5OH solutions, followed by heating at 200–400°C for 10 min–6 h in air, where the H2O/Ti(OC3H7 i )4 mole ratio (x) was varied from 1.0 to 8.0. The degree of crystallization and the crystallite size of the heat-treated TiO2 films were not significantly affected by the H2O content, while the surface structure became denser with an increase in x. The dense TiO2 films of x = 8.0 heated at 300–400°C for 6 h exhibited a refractive index of 2.22–2.25, which was higher than that of x = 1.0 heated at 800°C.