SPECIFIC FEATURES OF THE IR-SPECTRA OF SILICATE-GLASSES

The glassy state of matter, in contrast to crystalline solids, is char acterized by a lack of long-range order. In the structure of glasses, the bond lengths and bond angles are not fixed. As a consequence the v ibrational spectra of glassy substances exhibit various band shapes. T he bands in these spectra are characterized by complex shapes and sign ificant widths resulting in difficulties in the determination of the m ain spectral parameters, such as the number of bands, their positions and intensities. These difficulties limit the application of vibration al spectroscopy in the study of the structure of glasses. The main goa l of the present work is to show that an appropriate procedure of deco mposition of complex bands in the spectra makes it possible to obtain important information on the structure of solid glassy substances. The procedure proposed is based on (a) minimization of the number of band s, and (b) comparison with the spectra of crystalline analogues. The n umber of components in a complex band and its parameters are found by analysis of the second derivative of the spectrum, using Fourier self- deconvolution as proposed by Griffiths and Pariente (Trends Anal. Chem ., 5 (1986) 209). According to the procedure proposed, the spectra of the crystalline and glassy analogues of the following substances were decomposed: SiO2 (silica), K[AlSi2O6] (leucite) and Li[AlSi2O6] (spodu mene). This decomposition of the complex bands in the spectra of glass y substances meant that their structures could be more readily deduced . It was shown that as well as the bands corresponding to the crystall ine analogues in the spectra of glasses, there are bands responsible f or characteristic features of the structure of glasses.