Structural investigation of iron phosphate glasses using molecular dynamics simulation

The current study reports the first molecular dynamics models of iron phosphate glasses. Models were made for xFeO–(100 − x)P2O5 glasses with x = 30, 40 and 50 and for xFe2O3–(100 − x)P2O5 glasses with x = 30 and 40. This study also looks at the effects of mixed Fe2+/Fe3+ contents. The models are in good agreement with experimental results for nearest-neighbour distances and coordination numbers, and in reasonable agreement with X-ray and neutron diffraction structure factors. As expected the models contain a tetrahedral phosphate network with P–O distances of 1.50 ± 0.01 Å. The network connectivity is dominated by the expected Qn (where n is the number of bridging oxygen) corresponding to the O:P ratio. These are average Qn of 2.3 for 40FeO and 1.0 for 40Fe2O3 glasses respectively. Interestingly a small amount of non-network oxygen is found to be present in the 40Fe2O3 glass model. The Fe–O coordination is close to 4.5 in both FeO and Fe2O3 glass models, with Fe–O bond lengths of 2.12 Å and 1.89 Å respectively. The greater durability of xFe2O3–(100 − x)P2O5 glasses can be attributed to the lower content of P–O–P bonds and higher bond valence across Fe–O–P bonds. For 40Fe2O3 glass the Fe–Fe correlation shows a main peak at 5–6 Å in good agreement with the result from magnetic scattering which was interpreted in terms of speromagnetic order.