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Title: Iron phosphate glasses: structure determination and radiation tolerance
Authors: Jolley, Kenny
Smith, Roger
Keywords: Molecular dynamics
Iron phosphate glass
Radiation damage
Issue Date: 2015
Publisher: Elsevier B.V. (© The Authors)
Citation: JOLLEY, K. and SMITH, R., 2015. Iron phosphate glasses: structure determination and radiation tolerance. Nuclear Instruments and Methods in Physics Research B, 374, pp. 8-13.
Abstract: Iron phosphate glass (IPG) has gained recent interest for use in encapsulating radioactive waste for long term storage. In this work, we investigate 5 different compositions of iron phosphate glass. We consider amorphous structures of 3 known crystalline phases: Fe2+View the MathML source(P2O7)2, View the MathML source(P2O7)3 and Fe3+(PO3)3, and structures of IPG (40 mol% Fe2O3 and 60 mol% P2O5), with 4% and 17% Fe2+ ion concentrations. Using constant volume molecular dynamics (MD), we quench a set of structures for each glass composition, to find the optimal density structure. We found that the lowest energy structures of IPG with 4% and 17% concentration of Fe2+, have a density of 3.25 and 3.28 g/cm3 respectively. This is slightly higher than the experimentally measured values of 2.9 and 2.95 g/cm3 respectively. We also estimate an upper and lower bound on the melting temperatures of each glass, then for each glass, we simulate radiation damage cascades at 4 keV. The cascade structures can be in the form of either a concentrated thermal spike or more diffuse with sub-cascade branching. We found that the glass compositions with a higher Fe/P atomic ratio, contained a greater number of displacements after the cascade. We also found that the IPG with 4% Fe2+, contained slightly fewer displacements than the IPG with 17% Fe2+. This is consistent with our previous work, which showed that the threshold displacement energies are lower for glasses with a lower Fe2+ content. In all the simulations, many PO4 polyhedra are destroyed during the early stages of irradiation, but recover strongly over a time scale of picoseconds, leaving very few over or under co-ordinated P atoms at the end of the ballistic phase. This is in contrast to recent work in apatite. The strong recovery indicates that phosphate glasses with a low Fe2+ content could be good materials for waste encapsulation.
Description: This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)
Sponsor: The work was funded as part of a joint UK-India Nuclear Collaboration through EPSRC Grant No. EP/K007882/1.
Version: Published
DOI: 10.1016/j.nimb.2015.09.043
URI: https://dspace.lboro.ac.uk/2134/19202
Publisher Link: http://dx.doi.org/10.1016/j.nimb.2015.09.043
Appears in Collections:Published Articles (Maths)

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