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The environment of Fe3+/Fe2+ cations in a sodium borosilicate glass

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The neutron diffraction isotopic substitution technique is employed to investigate the environment of Fe3+/Fe2+ cations in a sodium borosilicate glass matrix of composition 0·210Na2O.0·18511B2O3.0·605SiO2. The neutron diffraction data were obtained using the D4c diffractometer at the Institut Laue-Langevin (ILL; Grenoble, France), and were recorded for three samples; the base glass, the base glass incorporating natural Fe2O3 (12 mol%) and a similar glass containing Fe2O3 enriched in 57Fe. The data are Fourier transformed to yield the real space total correlation function, T(r), and the first co-ordination shells of the Fe3+/Fe2+ cations are investigated via a peak fit to the isotopic difference correlation function ΔTFe(r). It is concluded that the iron is mainly present as Fe3+ cations, both tetrahedrally and octahedrally co-ordinated by oxygen atoms, plus a small fraction (0·07±0·01) of Fe2+ cations in octahedral co-ordination. The Fe3+ tetrahedral fraction is 0·45±0·10, and appears to exist as FeØ4 structural units incorporated into the network of silicate chemical groupings, with their negative charge being balanced by Na+ network modifying cations. The remaining Fe3+ cations (fraction 0·48±0·10) are thought to be predominantly octahedrally co-ordinated and associated with BO3– 3 orthoborate anions in FeBO3 chemical groupings, which become non-stoichiometric due to the reduction of some of the Fe3+ cations to Fe2+.

Document Type: Research Article

Publication date: June 1, 2017

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