On the coordination of iron ions in sodium borosilicate glasses: I. A wide angle X-ray diffraction investigation

Abstract

Three sodium borosilicate glasses, containing approximately 4%, 8% and 12% by weight of Fe 2O 3, have been investigated by X-ray diffraction technique in order to determine the structural arrangement of iron ions in these glasses. The radial distribution functions of the iron glasses have been compared to suitable distribution functions obtained from an appropriate iron-free sodium borosilicate matrix. The analysis of the resulting distribution difference curves leads to the unambiguous conclusion that in 4% and 8% glasses iron ions are surrounded by four oxygen atoms at the distance expected for a tetrahedral coordination. The structural arrangement of iron ions in the 12% glass is very likely to be the same, although the analysis of the data is complicated by an initial crystalline phase separation within the amorphous network. In addition to the structural parameters obtained for the first iron shell, a tentative model to explain the second order interactions around iron ions is discussed.