Analysis of strain and disordering kinetics based on combined RBS-channeling and X-ray diffraction atomic-scale modelling

Abstract

Ion beams delivered by particle accelerators are routinely used to emulate harsh, radiative environments and they also constitute the foundations of the modern microelectronics industry. To characterize irradiated materials, numerous experimental and computational techniques can be implemented, but it is extremely dicult to eectively intertwine them, and to compare the associated data. In the present work, we present an integrated, experimental and computational approach that uses a same set of molecular dynamics simulations to generate signals of Rutherford backscattering spectrometry in channelling condition and X-ray diraction, with UO 2 as a test-case material. From these signals, parameters to monitor the damage level are computed, compared and confronted with experimental data. Although the evolution of the strain and disordering kinetics obtained by simulations differ on an absolute scale from those obtained experimentally (a discrepancy inherent to the method used to generate the atomic-scale data), a very good relative agreement is obtained, which demonstrates the validity of the approach, hence providing a new tool for the ne study of irradiation eects in materials.

Structural Aspects of the Superionic Transition in AX2 Compounds With the Fluorite Structure

“…Two-dimensional single crystal diffraction patterns were generated using the approach described in ( Jin et al, 2020 ). So called reciprocal space maps (RSMs) were computed in the HHL planes, where H and L are non-integer multiples of the reciprocal lattice unit cell of a given fluorite structure , where is the lattice parameter of the AX 2 crystal at the considered temperature T .…”

Computational diffraction reveals long-range strains, distortions and disorder in molecular dynamics simulations of irradiated single crystals

“…It has proven very efficient for simulating irradiation damage in different oxides (Chartier et al, 2009;Catillon & Chartier, 2014) and graphite (Chartier et al, 2018). In the MD simulations, only uranium Frenkel pairs were created, which implies that the introduced disorder is measured in terms of displacement per uranium, dpU (Jin et al, 2020). MD calculations were performed in a 26 Â 26 Â 26 nm UO 2 cell (768 000 atoms, with periodic boundary conditions in the three dimensions) using a Morelon empirical potential (Morelon et al, 2003) which exhibits a relevant response to irradiation (Devanathan et al, 2010).…”

“…This observation points to a Frank ! perfect dislocation loop reaction mechanism (Chartier et al, 2016;Jin et al, 2020), which, every time it takes places, locally lowers (i.e. relaxes) the strain in the region surrounding the initial Frank loop, hence the abrupt character.…”

“…It is now well documented that the disordering kinetics of UO 2 exposed to ion irradiation can be divided into different stages corresponding to the different dominant defects in the MD cell (Chartier et al, 2016;Jin et al, 2020), namely Frenkel pairs (stage 1, from 0 to 0.09 dpU), Frank loops (stage 2, from 0.09 to 0.3 dpU), perfect loops (stage 3, from 0.3 to $1.5 dpU) and dislocation lines (stage 4, above $1.5 dpU). In these studies, it was also demonstrated that the different types of defects can be correlated with the evolution of both the average elongation strain and the average disorder.…”

“…Finally, we prove that both the reciprocal-space and the real-space (that is, directly from the atomic coordinates) long-range strain determinations yield the same results if longrange correlations are correctly taken into account. The validity of our computational diffraction approach is tested on UO 2 MD cells in which we simulated ion-irradiation-induced disorder and for which we have a good understanding of the defect structure and evolution (Chartier et al, 2016;Jin et al, 2020).…”