Iron phosphate glasses: Structure determination and radiation tolerance

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS

卷:374

Article

Jolley, Kenny¹  Smith, Roger¹ 

[1] Univ Loughborough, Math Sci, Loughborough LE11 3TU, Leics, England

关键词: Molecular dynamics;    Iron phosphate glass;    Radiation damage;   

DOI  :  10.1016/j.nimb.2015.09.043

来源: Elsevier

【 摘 要 】

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+Fe23+(P2O7)(2), Fe-4(3+)(P2O7)(3) and Fe3+(P(O-3)(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/cm(3) respectively. This is slightly higher than the experimentally measured values of 2.9 and 2.95 g/cm(3) 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. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

【 授权许可】

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