INFRARED-SPECTROSCOPY ANALYSIS OF THE LOCAL ATOMIC-STRUCTURE IN SILICA PREPARED BY SOL-GEL

Infrared spectroscopy has been used to analyze the structural changes in samples prepared by the sol-gel method. Silica gels were prepared f rom alcoholic solutions of tetraethylorthosilicate (TEOS) with differe nt H2O/TEOS molar ratios. The IR spectra of these gels, in the Si-O bo nd stretching region, shows that their structure strongly depends on t he H2O/TEOS ratio. The relative change in intensity of the Si-O stretc hing modes, in samples prepared using different H2O/TEOS ratios, are i nterpreted in terms of different degrees of structural disorder. Accor ding to our infrared absorption data, a decrease in the H2O/TEOS ratio from about 7, the SiO2 structure evolves from a three-dimensional net work toward a chainlike structure. (C) 1998 American Institute of Phys ics. [S0021-9606(98)70341-1].