INFRARED REFLECTANCE INVESTIGATION OF ALKALI DIBORATE GLASSES

Alkali diborate glasses have been investigated by infrared reflectance spectroscopy to demonstrate the potential of this technique for a quantitative description of the glass structure. Kramers-Kronig transformation was performed on the reflectance data to obtain the optical and dielectric properties of glasses over a broad and continuous spectral range (30-4000 cm-1). Analysis of the mid infrared spectra shows that the normalized absorption area attributed to boron-oxygen tetrahedra decreases upon increasing alkali cation ionic radius, and scales linearly with the fraction of four-coordinated boron atoms determined recently from NMR spectra. The far infrared asymmetric absorption profiles were deconvoluted into two broad bands and attributed to vibrations of alkali cations in two distinct network environments. Cation effective charges were calculated from the integrated absorption of the bands due to cation vibrations, and were found to increase with alkali ionic radius.