Dynamical simulations of radiation damage in magnesium aluminate spinel, MgAl2O4

Collision cascades in MgAl2O4 are investigated using molecular dynamics simulations in order to determine the threshold displacement energies, Ed, and the damage imparted to the lattice at energies of up to 5 keV. The value of Ed is determined for MgAl2O4 on each of the Mg, Al and O sublattices for different orientations of the primary knock-on atom (PKA). The lowest Ed required to create permanent defects was for an O PKA along the direction with a value of 27.5 eV, while the highest was 277.5 eV along for an Mg PKA. Higher energy cascades show that a much wider variety of defects remain after the collisional phase than for similar cascades in MgO but the number of Frenkel pairs produced is smaller. The predominant defects that form are antisite defects on the cation sublattice only and O and Mg split interstitials orientated along the direction. Some Mg–Al split interstitials centred on an Mg site were also observed. However, some more extended defect complexes can also arise which have no well defined structure.