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.
The radiation response of perfect crystals of MgAl 2 O 4 , partially inverted MgGa 2 O 4 and fully inverse MgIn 2 O 4 were investigated using molecular dynamics. Dynamical cascades were initiated in these spinels over a range of trajectories with energies of 400 eV and 2 keV for the primary knock-on event. Collision cascades were set up on each of the cation and anion sublattices and were monitored up to 10 ps. Simulations in the normal MgAl 2 O 4 spinel for the 2 keV energy regime resulted in similar defect structures as obtained at the post-threshold 400 eV energies, with little clustering occurring. The predominant defect configurations were split interstitials and cation antisites. For the inverse spinels, a much wider variety of lattice imperfections was observed. More defects were also produced due to the formation of interstitialvacancy cation chains and oxygen crowdions.
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