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)P(2)O(5) glasses with x=30. 40 and 50 and for xFe(2)O(3)-(100 x)P(2)O(5) glasses with x = 30 and 40. This study also looks at the effects of mixed Fe(2+)/Fe(3+) 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 angstrom. The network connectivity is dominated by the expected Q(n) (where n is the number of bridging oxygen) corresponding to the O:P ratio. These are average Q(n) of 2.3 for 40FeO and 1.0 for 40Fe(2)O(3) glasses respectively. Interestingly a small amount of non-network oxygen is found to be present in the 40Fe(2)O(3) glass model. The Fe-O coordination is close to 4.5 in both FeO and Fe(2)O(3) glass models, with Fe-O bond lengths of 212 angstrom and 1.89 angstrom respectively. The greater durability of xFe(2)O(3)-(100 x)P(2)O(5) glasses can be attributed to the lower content of P-O-P bonds and higher bond valence across Fe-O-P bonds. For 40Fe(2)O(3) glass the Fe-Fe correlation shows a main peak at 5-6 angstrom in good agreement with the result from magnetic scattering which was interpreted in terms of speromagnetic order. (C) 2010 Elsevier B.V. All rights reserved.