The direct consequence of irradiation on a material was the creation of point defects—typically interstitials and vacancies, and their aggregates—but it was the ultimate fate of these defects that determines the material's radiation tolerance. Thus, understanding how defects migrate and interact with sinks, such as grain boundaries, was crucial for predicting the evolution of the material. Defect properties of two polymorphs of TiO2, rutile and anatase, were examined in order to determine how these materials might respond differently to irradiation. Using molecular statics and temperature accelerated dynamics, attention was focussed on two issues: how point defects interacted with a representative grain boundary and how they migrated in the bulk phase. It was found that grain boundaries in both polymorphs were strong sinks for all point defects, though somewhat stronger in rutile than anatase. Further, the defect kinetics were very different in the two polymorphs, with interstitial species diffusing quickly in rutile while oxygen defects, both interstitials and vacancies, were fast diffusers in anatase. These results permitted speculation as to how grain boundaries would modify the radiation tolerance of the materials. In particular, grain boundaries in rutile will lead to a space charge layer at the boundary and a vacancy-rich damage structure, while in anatase the damage structure would likely be more stoichiometric, but with larger defects consisting primarily of Ti ions.

Defects in Rutile and Anatase Polymorphs of TiO2: Kinetics and Thermodynamics near Grain Boundaries. Uberuaga, B.P., Bai, X.M.: Journal of Physics - Condensed Matter, 2011, 23[43], 435004