Structural Study of Alkaline Earth Aluminosilicate Glasses by Vibrational Spectroscopy

Abstract

Understanding the structure of alkaline earth aluminosilicate glasses is important for many applications including better interpretation of the structure property correlation and subsequent development of commercial glasses for various technologies including damage resistant and stronger glasses for consumer electronics, photonics, nuclear waste sequestration, bioglasses, and new glasses in life science. Changes in the coordination of aluminate polyhedra, connectivity and the degree of polymerization of the network impact the materials physical properties. The structure of two alkaline earth aluminosilicate glass series is studied by Infrared and Raman spectroscopy. The glasses contain either barium or magnesium oxide as modifier components. Multiple glasses were available for each series with the formula: xMO-yAl2O3-(100-x-y)SiO2. The aluminum coordination was quantified by 27Al-NMR, confirming a predominant four-fold coordination. However, the high field strength of Mg2+ compared to Ba2+ has a significant impact on the aluminum speciation as more five-fold coordinated Al, up to 14%, as well as higher disporportionation in the glass and more non-bridging oxygen ions in the Mg-glasses. Nevertheless, the higher crosslinking strength of Mg2+, is reflected in a higher Tg. The magnesium coordination was deduced from oxygen polarizabilities and found to be closer to six-fold coordinated. Increasing non-bridging oxygen formation with increasing modifier, both Mg and Ba, is seen by the increasing peak intensities of the Q2 and Q3 modes for both glass series, resulting in a decrease in connectivity of the network with increasing modifier content.