Environment of ferrous iron in CaFeSi2O6 glass; contributions of EXAFS andmolecular dynamics

The understanding of the structural effects of iron in amorphous systems is of primary importance in the design of technological glasses and for ratio nalising 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-r ay absorption fine structure (EXAFS) spectroscopy and molecular dynamics (M D) simulations. Ferrous iron is located in sites with a distribution of Fe- O distances. with typical geometries close to a tetrahedron and to a triang ular bipyramid. At medium-range order, the presence of calcium and iron as next nearest neighbours is found in the experimental data and in the simula tions. The iron polyhedra are apex-connected to the silicate network, while edge-linked to each other and to calcium-polyhedra. The occurrence frequen cy of these edge-sharing polyhedra is that expected for a random distributi on or a limited segregation of iron in the glass. (C) 2000 Elsevier Science B.V. All rights reserved.