ATOMISTIC SIMULATIONS OF CERAMIC MATERIALS RELEVANT FOR NUCLEAR WASTE MANAGEMENT: CASES OF MONAZITE AND PYROCHLORE

摘要

We performed systematic ab initio atomistic simulations of monazite (LnPO4) and pyrochlore (A2B2O7)-type ceramics. The simulated properties include the themiodynamic parameters, the threshold displacement energies, the elastic constants and the energies of defects formation. We computed the excess effects of mixing in various monazite-type solid solutions and provided crucial information on their thermodynamic stability. To better understand the radiation damage resistance of the considered novel waste forms, we simulated the threshold displacement energies and the displacement probabilities of La cation in LaPO4 monazite and computed defect formation energies in various pyrochlore compounds. The observed exothermic character of the anion Frenkel pair defects suggests that the ease of the defect formation correlates with instability of the pyrochlore structure relative to fluorite. Further calculations of activation barriers for the oxygen migration shed a light on the mechanism of the order-disorder transition in pyrochlore compounds.