The propensity of a primary knock-on atom to produce defects in zircon was investigated by molecular dynamics simulations. The dynamic behavior of highly directed collision sequences in each of the sub-lattices was examined for a range of energies up to 200eV. The energy range was limited by the system size, which in turn was limited by the long-range interactions of the potential model. For the heavier ions, both homogeneous and heterogeneous collision sequences lead to the dissipation of large amounts of energy and to defect formation. There was a large range of energy before the first displacement event occurred, which was much larger for the cations than for the anion, where the energy was absorbed into the lattice without damage formation. Above the minimum threshold displacement energy there was another range of energy up to 200eV for which formation damage was relatively constant. The limitations in the system size, and therefore on the primary knock-on atom energies, does not allow for a thorough search of a second distinct displacement event in the same direction. In some cases, no damage occurred for energies up to 200eV. The O anions were seen to have a stronger response to the motion of the Si cations as compared to the motion of the Zr cation due to the stronger binding energy of Si with O. Consequently, Si atoms maintain their tetrahedral coordination, whereas Zr atoms could reduce their coordination number without a great loss of stability.

Molecular-Dynamics Simulation Study of Threshold Displacements and Defect Formation in Zircon. B.Park, W.J.Weber, L.R.Corrales: Physical Review B, 2001, 64[17], 174108 (16pp)