Molecular-dynamics simulation study of threshold displacements and defect formation in zircon - art. no. 174108

The propensity of a primary-knock-on-atom (PKA) to produce defects in zirco n is investigated by molecular-dynamics simulations. The dynamic behavior o f highly directed collision sequences in each of the sublattices is examine d for a range of energies up to 200 eV. The energy range is limited by the system size, which in turn is 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 is a large range of energy before the first disp lacement event occurs, which is much larger for the cations than for the an ion, where the energy is absorbed into the lattice without damage formation . Above the minimum threshold displacement energy there is another range of energy up to 200 eV for which formation damage is relatively constant. The limitations in the system size, and therefore on the PKA energies, does no t allow for a thorough search of a second distinct displacement event in th e same direction. In some cases, no damage occurs for energies up to 200 eV . The oxygen anions are seen to have a stronger response to the motion of t he silicon cations as compared to the motion of the zirconium cation due to the stronger binding energy of Si with O. Consequently, silicon atoms main tain their tetrahedral coordination, whereas zirconium atoms can reduce the ir coordination number without a great loss of stability.