Optical and mechanical properties of sol–gel silica–titania hard optical coatings derived from methyltrimethoxysilane and tetrapropylorthotitanate as precursors

Abstract Silica–titania hard optical coatings based on titania/organically modified silane composite materials were prepared by the sol–gel spin coating technique. Acid catalyzed solutions of methyltrimethoxysilane mixed with tetrapropylorthotitanate were used as precursors for the silica–titania coatings. Atomic force microscopy, thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy have been used to investigate the optical and structural properties of the coatings. The results indicated that purely inorganic and crack-free silica–titania coatings could be obtained after heating at a temperature of 500 °C or higher. The hardness and Young’s modulus of the coatings were characterized by a nanoindenter and they showed a dependence on the heat-treatment temperature and titanium content. Hardness as high as about 7.0 GPa was observed in a high titanium content coating heat-treated at 800 °C.