Structural characterization of iron–alumino–silicate glasses

Two series of aluminosilicate glasses containing Fe ₂O ₃ were investigated. In the first one, the Fe ₂O ₃ content was 1.5 mol%, and (Al ₂O ₃ + Na ₂O) was substituted for SiO ₂. Na ₂O was added with Al ₂O ₃ in order to keep constant the network polymerization. In the second series, the Fe ₂O ₃ content was 4.4 mol%, and CaO was substituted for Na ₂ O in order to observe the effect of the cations for the charge compensation of tetrahedra. X-ray absorption near-edge spectroscopy at Fe K-edge, Mössbauer spectroscopy and electron spin resonance indicated that both Fe ³⁺ tetrahedral and octahedral coordinations are present in all the glasses. The quantity of octahedral Fe ³⁺ decreases with increased quantity of (Al ₂O ₃ + Na ₂O), and with the substitution of CaO for Na ₂ O. This is explained by the influence of the glass basicity on Fe ³⁺ coordination.