Modification of the Fe-environment in Fe2O3 glass/glass ceramic systems containing Pb, Na and Si

Abstract

The effect of composition and casting temperature on the microstructure and the oxidation state of Fe in a series of glass/glass ceramic materials that contain Fe2O3, PbO, Na2O and SiO2 is studied by means of X-ray fluorescence mapping (XRF), micro- (μ-) and conventional X-ray absorption fine structure (XAFS) and 75Fe Mössbauer spectroscopies. The Mössbauer results reveal that the majority of Fe exists in the Fe3+ state. Divalent Fe is detected only in small amounts (2.1–5.7at.%) in the ternary samples consisting of Fe2O3, SiO2 and Na2O. The XRF mapping demonstrates that the ternary samples Fe2O3–Na2O–SiO2 that contain more than 40wt.% of Fe2O3 develop Fe-rich islands. According to the combined μ-EXAFS and EXAFS results, 44wt.% of the Fe atoms belong to those Fe-rich microcrystalline islands, where they are octahedrally coordinated, while the rest belong to the vitreous matrix where they are tetrahedrally coordinated. The Fe–O distance is found equal to 0.188nm and 0.193nm in the vitreous and microcrystalline regions, respectively. The differences in the NEXAFS spectra, due to the different local environment of Fe embedded in the vitreous or microcrystalline regions, are also discussed.