Effects of the Iron Content and Redox State on the Structure of Sodium Borosilicate Glasses: A R aman, M össbauer and Boron K‐Edge XANES Spectroscopy Study

The structure of iron‐bearing sodium borosilicate glasses with up to 10 mol% “ FeO ” has been investigated in the range 0.15 < Fe 3+ /Σ Fe < 0.95. According to M össbauer spectroscopy, Fe 3+ and Fe 2+ are mainly in tetrahedral and octahedral coordination, respectively, although other coordination states exist for both cations. From XANES experiments, we conclude that increasing Fe content and varying redox states have only a minor effect on the relative proportions of BO 3 and BO 4 units. In R aman spectra, a decrease of the proportion of BO 4 species present in danburite‐like units ( Na 2 O · B 2 O 3 ·2 SiO 2 ) is found upon increasing iron content and oxidizing state. Whereas the insensitivity of the overall boron speciation to iron content and redox state points to weak interactions between boron and iron, the changes affecting BO 4 species do indicate a more subtle interplay between Fe 3+ and the other tetrahedrally coordinated cations ( Si , B ) because of the competition between tetrahedral Fe 3+ and B 3+ for charge compensation by Na + .