Structural role and coordination environment of Fe in Fe2O3-PbO-SiO2-Na2O composite glasses

The structural role, coordination geometry and valence of Fe in a series of Fe2O3-PbO-SiO2-Na2O glasses are studied by means of Fe-K-NEXAFS and EXAFS spectroscopies. Parameters for the study are the concentration of the Fe and Pb-oxides, the SiO2/Na2O ratio and the cast temperature. The EXAFS and NEXAFS results reveal that the role of Fe3+ depends on the concentration of Fe2O3. More specifically, in most of the studied quaternary systems, the Fe3+ ion is a glass former, i.e. the Fe atoms belong to FeO4 tetrahedra that participate in the formation of the glassy network. The role of Fe as an intermediate oxide is identified only in one sample with 20 wt% Fe2O3, where similar to 80 at.% of the Fe atoms are tetrahedrally coordinated with O atoms, while the remaining similar to 20 at.% of the Fe atoms occupy octahedral sites. It is also revealed that the tetrahedral coordination of Fe in the vitreous matrix is destroyed when a number of parameters is altered, such as the T-cast, the (Fe + Si)/O and the SiO2/Na2O ratio. (C) 2007 Elsevier B.V. All rights reserved.