Simulation of defects and defect processes in fluorite and fluorite related oxides: Implications for radiation tolerance

Atomic scale computer simulation is used to study four defect related processes across a broad range of A23+B24+O7 composition that exhibit pyrochlore or the parent fluorite structures. The first set of results concern the energy for a local disorder process, through which the compositional ranges of stability of the structures are discussed. Second, the propensity of a given composition to exhibit either trivalent excess or tetravalent excess non-stoichiometry is considered. Third, the volume expansion upon transformation from pyrochlore to fluorite or pyrochlore to amorphous is presented. Lastly, the activation energy for oxygen ion migration is determined and the migration mechanisms considered. All these processes have a bearing on the propensity of a composition to resist radiation induced amorphisation. By considering the relative energies and volume changes as a function of composition these simulations identify regions of compositional significance.