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

AbstractIron 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 40mol% Fe2O3 and 60mol% 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 2.5Å respectively. The threshold displacement energy (Ed) 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