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%, Sn O2/(SnO2 + SiO2). Glasses with higher Sn content ( greater than or equal to 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 t o understand the mechanism, at molecular level. which gives rise to substit utional Sn-doping or to SnO2 clustering. It was found that the hydrolysis o f DBTDA was faster than TEOS. Hydrolyzed DBTDA acted as a crosslinker betwe en molecules of hydrolyzed TEOS. Since tin atoms preferentially link to sil icon atoms via bridging oxygens, no aggregation of Sn atoms occurred in sot and gel phases. Also in the Sti-doped SiO2 samples with Sn content greater than or equal to 1.6 wt% no aggregation of Sn atoms was observed in the xe rogels. Segregation of SnO2 occurred during the thermal treatment to obtain glass. (C) 2001 Elsevier Science B.V. All rights reserved.