STUDY OF XEROGEL-GLASS TRANSITION OF CUO SIO2

The xerogel-glass transition of SiO2 containing various amounts of CuO was studied by thermogravimetry, differential thermal analysis, Fouri er transform infrared spectroscopy, diffuse UV-VIS-NIR reflectance, el ectron spin resonance spectroscopy, and X-ray photoelectron spectrosco py. The samples were prepared by the sol-gel process from tetraethoxys ilane, and copper(II) acetate monohydrate. Significant structural chan ges were observed during the various stages of glass formation. It was concluded that copper(II) ions exist in two different enviroments, i. e., isolated and clustered. The results indicate that the former remai ns entrapped (doped) in the xerogel and glass, and that the clustered copper(II) ions were transformed into highly dispersed CuO by calcinat ion. The relative amounts of these species depend on the copper(II) co ncentration and, except for the sample with 0.5% CuO, the amount of is olated copper(II) ions is lower than that of the clustered ions. (C) 1 996 Academic Press, Inc.