Structures of silicate glasses with varying sodium and fixed iron contents

Abstract

Silicate glasses have been synthesised with a fixed 8 mol% of Fe3O4 and sodium oxide varying from 12 mol% to 20 mol%. The environment of the Fe ion was examined by Extended X-ray Absorption Fine structure and Mössbauer spectroscopy which have shown tetrahedral coordination of oxygen around Fe regardless of the oxidation state of iron. Mössbauer data indicate increasing; distortion of these tetrahedral units and Fe3+ to Fe2+ ratios, with increasing sodium concentration. Raman spectroscopic studies have shown the presence of Qn linkages for n = 0 to n = 4. For the sodium silicate glass without iron, the single most common linkage is Q3 (~ 50%) suggesting the role of the alkali to be disruptive to the continuity of the silica random network. For the iron containing glasses, the main linkage is Q2 (~ 65%). However, in the latter glasses the fraction of Q3 linkages although considerably less (~10% to ~20%) than Q2 is shown to increase with alkali content due to the concomitant rise of Fe3+ ions which are known to be network formers.