Environment of ferrous iron in CaFeSi2O6 glass; contributions of EXAFS and molecular dynamics

The understanding of the structural effects of iron in amorphous systems is of primary importance in the design of technological glasses and for rationalising the dynamic properties of volcanic processes and glass formation. In the present work, the local and medium-range environment of iron in the totally reduced oxide glass CaFeSi2O6 are studied by combining extended X-ray absorption fine structure (EXAFS) spectroscopy and molecular dynamics (MD) simulations. Ferrous iron is located in sites with a distribution of Fe–O distances, with typical geometries close to a tetrahedron and to a triangular bipyramid. At medium-range order, the presence of calcium and iron as next nearest neighbours is found in the experimental data and in the simulations. The iron polyhedra are apex-connected to the silicate network, while edge-linked to each other and to calcium-polyhedra. The occurrence frequency of these edge-sharing polyhedra is that expected for a random distribution or a limited segregation of iron in the glass.