57Fe Mossbauer spectroscopy and magnetic susceptibility of iron alkali silicate glasses

The structure and properties of iron alkali silicate glasses depend to a large extent on the structural role of iron such as its valence state and coordination. Both are a function of the oxygen fugacity, the total amount of iron present and the amount and type of alkalis as well as pressure, temperature and quenching sate. This paper addresses the structural role of iron as a function of alkalis and alkali content. Silicate glasses in the systems SiO2-Fe2O3-R2O (R: Li, Na, K) (SFL, SFN and SFK) each with 5 mol% Fe2O3 were investigated by Mossbauer spectroscopy and magnetic measurements (SQUID). In SFN and SFK glasses Fe3+ is in tetrahedral coordination. A comparison with spectra from corresponding crystals suggests that in SFL glasses some Fe3+ is in a coordination higher than fourfold In spite of the synthesis in air SFL and SFN glasses contain Fe2+ with 5-10% of the total iron, occurring in octahedral coordination. All glasses are paramagnetic down to 5 K.