Georges Calas FSGT is University Institute of France Chair of Mineralogy at the Pierre & Marie Curie University in Paris. His research centers on structural properties of materials linked to the presence of minor components and impurities or radiation-induced defects. This helps rationalize how the molecular-scale organization of minerals, glasses, and melts controls their properties, with applications in environmental and materials sciences, including cultural heritage, functional glasses and nuclear waste materials.
Some aspects of iron spectroscopy in glasses
Georges Calas*, Laurent Cormier, Laurence Galoisy, Gérald Lelong
Institute of Mineralogy, Physics of Materials and Cosmochemistry, Université P&M Curie, Paris, France.
Iron has always been an element of considerable interest in glass science and technology, present as an unwanted impurity or intentionally added to develop peculiar glass and melt properties. In addition to control the redox state of industrial and natural silicate melts and glasses, its divalent and trivalent oxidation states control numerous major physical and chemical properties such as melt structure, viscosity, glass color, heat transfer, thermal control and solar glasses, gas dissolution, etc… On most applications, there is a need to understand iron speciation, mostly the redox state and the local structure around each oxidation state. A positive point is that ferrous and ferric iron may be investigated by several spectroscopic and diffraction methods. However, in order to get a consistent picture, it is necessary to cross-link the results obtained by these various approaches and to compare them to the scenarios provided by numerical modeling.
We will briefly review data provided by spectroscopic methods such as optical absorption spectroscopy, XANES and HERFD-XANES, EXAFS, Mössbauer effect and EPR and by neutron diffraction with isotopic substitution. In addition to information on Fe-speciation and the influence of glass composition and synthesis conditions, there is a large influence of the medium-range organization of the glass. Prevalence of distribution effects, presence of “exotic” sites, need for focusing more on site geometry than on coordination number or the relevance of “crystalline references” constitute some aspects which will be discussed.