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Iron oxide is commonly found in natural or industrial glass compositions and can exist as ferrous (Fe2+) or ferric (Fe3+) species, with their ratios depending on glass composition, temperature, pressure and the redox reactions during the glass forming process. The iron redox ratio plays an important role on silicate glass structures and consequently various properties. This work aims to study the effect of iron oxide, and particularly the iron redox ratio, on the structures of borosilicate and boroaluminosilicate glasses using molecular dynamics simulations with newly developed iron potential parameters that are compatible with the borosilicate potentials. The results provide detailed cation coordination states of both iron species and the effect of redox ratio on boron coordination and other structural features. Particularly, competition for charge compensating modifier cations (such as Na+) among the fourfold‐coordinated cations such as B3+, Al3+, and Fe3+ is investigated by calculating the cation–cation pair distribution functions and coordination preferential ratios. The results show that the trivalent ferric ions, with a shorter Fe–O bond distance and better defined first coordiation shell with mainly four‐fold coordination, act as a glass former whereas the divalent ferrous ions mainly play the role of glass modifier. The ferrous/ferric ratio (Fe2+/Fe3+) was found to affect the glass chemistry and hence glass properties by regulating the amount of four‐coordinated boron, the fraction of non‐briding oxygen and other features. The results are compared with available experimental data to gain insights of the complex structures and charge compensation schemes of the glass system. [ABSTRACT FROM AUTHOR]

• Molecular dynamics simulations of sodium iron silicate glasses with different compositions and measured redox ratios. • Short and medium range structures obtained and structural role of iron determined from simulation results. • Ferric iron is mainly four-fold coordinated and plays the role of glass former while ferrous iron has higher coordination and plays the role of modifier. • Iron local environments form simulations agree well with those measured from EXAFS measurements. • Glass structure were compared with the melt structure and the effect of temperature and redox ratio studied. Iron oxides are frequently found in natural and industrial glass compositions and can affect various physical and chemical properties of the glasses and their melts. Thus, a fundamental understanding of iron-bearing silicate melts and glasses is of both scientific and technological importance. This study investigates the structures of sodium iron silicate glasses with compositions of NaFeSiO 4 , NaFeSi 2 O 6 , NaFeSi 3 O 8 , and Na 5 FeSi 4 O 12 using molecular dynamics simulations in combination with Extended X-ray Absorption Fine Structure (EXAFS) characterizations. Short and medium range structural features of these glasses support that ferrous (Fe2+) and ferric (Fe3+) ions play the roles of network modifier and network former, respectively, with the Fe oxidation states playing an important role in the polymerization of the glass network. These simulation results agree well with newly measured room temperature EXAFS spectra. The simulated glass structures were also compared to the melts structures with the same composition but different redox ratios. The average coordination numbers of the cations were found to be affected both by the melt temperature and iron redox ratio. [ABSTRACT FROM AUTHOR]