Native vacancy migrations in zircon

Energy minimization methods were used to simulate the migration of Zr, Si, and O vacancies in zircon (ZrSiO 4). Two sets of interatomic potentials were employed for comparison: one with O–Si–O three-body terms for the SiO 4, and one without. Results for Si were inconclusive, but consistent with maintaining the integrity of the SiO 4 molecular units. Both Zr and O vacancies can migrate on three-dimensional sublattice networks, thus supporting the experimentally observed diffusional isotropy. The predicted Zr vacancy migration energy (1.16–1.38 eV) was in good agreement with experiment if supplemented by Zr vacancy formation via Schottky or Frenkel defects (6.21–12.28 eV/defect). Oxygen vacancy migration energies were predicted to be 0.99–1.16 eV, somewhat lower than the experimental value of 4.64 eV measured in natural zircons, which thus may include significant contributions from vacancy formation mechanisms at 3.31–6.52 eV/defect.