Multi-timescale investigation of radiation damage near TiO₂ rutile grain boundaries

Abstract

To understand the interactions between defects and grain boundaries (GBs) in oxides, two atomistic modeling methods were used to examine the role of GBs in a model system, rutile TiO₂, in modifying radiation-induced defect production and annealing. Molecular dynamics was used to investigate defect production near a symmetric tilt GB at both 300 K and 1000 K. The damage production is found to be sensitive to the initial distance of the primary knock-on atom from the GB. We find three distinct regimes in which GBs have different effects. Similar to GBs in metals, the GB absorbs more interstitials than vacancies at certain distances while this behavior of biased loading of interstitials diminishes at other distances. Further, we obtain the statistics of both interstitial and vacancy clusters produced in collision cascades in terms of their compositions at two temperatures. Perfectly stoichiometric defect clusters represent a small fraction of the total clusters produced. Moreover, a significant reduction in the number of interstitial clusters at 1000 K compared to 300 K is thought to be a consequence of enhanced migration of interstitials towards the GB. Finally, the kinetic properties of certain defect clusters were investigated with temperature accelerated dynamics, without any a priori assumptions of migration mechanisms. Small interstitial clusters become mobile at high temperatures while small vacancy clusters do not. Multiple migration pathways exist and are typically complex and non-intuitive. We use this kinetic information to explain experimental observations and predict their long-time migration behavior near GBs.

Keywords:

• irradiation effects
• atomistic simulation
• grain boundaries
• defect cluster diffusion
• titanium dioxide
• multi-time scale modeling

Acknowledgements

This work is sponsored by the Center for Materials at Irradiation and Mechanical Extremes (CMIME), an Energy Frontier Research Center (EFRC) funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number 2008LANL1026. The analysis of the defect cluster mobility performed by X.M.B. was conducted under his present employment in the Center for Materials Science of Nuclear Fuel (CMSNF) at Idaho National Laboratory, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number FWP 1356. Los Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396. This manuscript has been co-authored by Battelle Energy Alliance, LLC under Contract No. DE-AC07-05ID14517 with the U.S. Department of Energy.