Substitutional tin-doped silica glasses: an infrared study of the sol–gel transition

A new sol–gel route using tetraethoxysilane (TEOS) and dibutyltindiacetate (DBTDA) as precursors allowed the preparation of Sn-doped SiO2 glasses with a content of substitutional Sn atoms in regular Si sites up to 1.4 wt%, SnO2/(SnO2+SiO2). Glasses with higher Sn content (⩾1.6 wt%) showed a crystalline nanophase of SnO2 dispersed throughout the silica matrix. The hydrolysis and condensation reactions of TEOS and DBTDA were investigated by FTIR spectroscopy during sol–gel transition in order to understand the mechanism, at molecular level, which gives rise to substitutional Sn-doping or to SnO2 clustering. It was found that the hydrolysis of DBTDA was faster than TEOS. Hydrolyzed DBTDA acted as a crosslinker between molecules of hydrolyzed TEOS. Since tin atoms preferentially link to silicon atoms via bridging oxygens, no aggregation of Sn atoms occurred in sol and gel phases. Also in the Sn-doped SiO2 samples with Sn content ⩾1.6 wt% no aggregation of Sn atoms was observed in the xerogels. Segregation of SnO2 occurred during the thermal treatment to obtain glass.