STRUCTURAL INFLUENCE OF NITROGEN IN ALKALINE-EARTH ALUMINOSILICATE GLASSES - IR ABSORPTION-SPECTROSCOPY

Glass samples with the formular composition M0.37Si0.53A10.10O1.58-3x/2Nx (M = Mg, Ca or Ba) have been studied by IR absorption spectroscopy, The nitrogen-free glass structure is built up with SiO4 and AlO4 linked units as in the metasilicate glasses. The M2+ cations are network modifiers, except Mg2+, which participates in the formative network inducing some of the Al3+ cations to exist in sixfold coordination and to play the role of network modifiers. The presence of nitrogen leads to very high cross-linkage of the aluminosilicate chain, forming a three-dimensional network where M2+ cations are inserted into increasingly larger sites (magnesium to barium glasses). The structural evolution could be correlated with physical properties: the network rigidity increases from barium to magnesium glasses and with the amount of nitrogen, and the disorder was emphasized with an increasing amount of nitrogen, but especially from magnesium to barium glasses; this explained the increase in the size of the vitreous domain in the Mg --> Ca --> Ba series.