Iron phosphate glasses: Structure determination and displacement energy thresholds, using a fixed charge potential model

Iron phosphate glass is a versatile matrix for the immobilisation of various radioactive elements found in high-level nuclear waste (HLW). Quenched glass structures of iron phosphate glasses with Fe/P ratios of 0.33, 0.67 and 0.75 and with a composition of 40 mol% Fe2O3 and 60 mol% P2O5, with 4% and 17% Fe2+ ion concentrations were generated using molecular dynamics and the threshold displacement energies calculated. In the minimum energy structures, we found that in nearly all cases the P atoms were 4-fold coordinated. The potential energy per atom increased with increasing concentration of Fe2+ ions with similar Fe/P ratio, suggesting that decreasing the Fe2+ content is a stabilising factor. The average bond distances between Fe2+-O, Fe3+-O, P-O and O-O were calculated as 2.12, 1.88, 1.5 and 2.5 angstrom respectively. The threshold displacement energy (E-d) was found to be dependent upon the ion specie, less for Fe2+ ions compared to Fe3+ ions, and was overall slightly lower than that determined for borosilicate glass. (C) 2015 The Authors. Published by Elsevier B.V.