Our latest paper is now available from the Journal of Materials Chemistry A site:

• E.E. Jay, P.M. Fossati, M.J.D. Rushton and R.W. Grimes, “Prediction and Characterisation of Radiation Damage in Fluorapatite”, Journal of Materials Chemistry A, (2014) doi:10.1039/C4TA01707B

In this paper we performed threshold displacement energy calculations and full damage cascades for the fluorapatite structure using molecular dynamics in conjunction with effective pair potentials. Fluorapatite is being considered as a host for the long term immobilisation of halide bearing nuclear wastes. As a result it is important to understand how the apatite structure withstands and recovers from radiation damage. Of particular interest were the structural changes noted in our damaged structures: phosphate polyhedra were found to form polymer chains, typical of phosphate glasses, that were interwoven with the calcium metaprisms forming the backbone of the apatite structure. The coincidence of these amorphous and crystalline features should help in our further understanding of the long term durability of this material.

Abstract

Molecular dynamics simulations, used in conjunction with a set of classical pair potentials, have been employed to examine simulated radiation damage cascades in the fluorapatite structure. Regions of damage have subsequently been assessed for their ability to recover and the effect that damage has on the important structural units defining the crystal structure, namely phosphate tetrahedra and calcium meta-prisms. Damage was considered by identifying how the phosphorous coordination environment changed during a collision cascade. This showed that PO₄ units are substantially retained, with only a very small number of under or over coordinated phosphate units being observed, even at peak radiation damage. By comparison the damaged region of the material showed a marked change in the topology of the phosphate polyhedra, which polymerised to form chains up to seven units in length. Significantly, the fluorine channels characteristic of the fluorapatite structure and defined by the structure’s calcium meta-prisms stayed almost entirely intact throughout. This meant that the damaged region could be characterised as amorphous phosphate chains interlaced with regular features of the original undamaged apatite structure.