Molecular dynamics study of UO₂ symmetric tilt grain boundaries around [001] axis

Abstract

Molecular dynamics and CRG empirical potential are used in this work to study the symmetrical tilt grain boundaries around the [001] axis in UO2. The analysis of atomic structures obtained by simulation shows excellent agreement with the Read and Schokley model (Read WT, Shockley W. Dislocation Models of Crystal Grain Boundaries. Physical Review. 1950;78:275) predicting the existence of regular dislocations in these grain boundaries. We calculated their energy of formation and cleavage as well as the energy of formation of Schottky defects and incorporation of xenon and krypton atoms in their proximity. This allowed us to determine how these properties evolve for this series of grain boundaries presenting similar geometric characteristics, as a function of the misorientation angle. In addition, the boundary between small and large misorientation grain boundaries has been determined around 20°, close to the value of 15° reported in literature.

A molecular dynamics survey of grain boundary energy in uranium dioxide and cerium dioxide

“…In general, annealing leads to lower GB energies and a smaller fluctuation in the results. The good agreement between fitted and MD results indicates that the dislocation‐based BRK functions are applicable for UO 2 , which is consistant with a recent MD study that demonstrated the dislocation structures in UO 2 GBs 12 …”

“…The good agreement between fitted and MD results indicates that the dislocation-based BRK functions are applicable for UO 2 , which is consistant with a recent MD study that demonstrated the dislocation structures in UO 2 GBs. 12 The energies of three 2D GB sets, the <100>, <110>, and <111> ATGBs, are plotted in Figures 5 and 6 as functions of the misorientation angle, ξ, and the asymmetry angle, η. The energies of the ATGBs are fitted to Equation (5) for <100>, Equation ( 6) for <110>, and Equation ( 7) for <111>, respectively.…”

“…For example, a positive correlation between GB thermal resistance and GB energy in CeO 2 , which is a commonly studied surrogate ceramic for UO 2 , has been suggested by molecular dynamics (MD) simulations 6 . Also, the cleavage energy for intergranular fracture in UO 2 has been shown to decrease with increasing GB energy 11,12 . The percolation paths for gas release are likely comprised of high energy GBs, which favor gas bubble nucleation and growth 13 .…”

“…6 Also, the cleavage energy for intergranular fracture in UO 2 has been shown to decrease with increasing GB energy. 11,12 The percolation paths for gas release are likely comprised of high energy GBs, which favor gas bubble nucleation and growth. 13 Therefore, there is a critical need to understand GB energy and its anisotropy in UO 2 .…”

A Molecular Dynamics Survey of Grain Boundary Energy in Uranium Dioxide and Cerium Dioxide

“…For example, a positive correlation between GB thermal resistance and GB energy in CeO2, which is a commonly studied surrogate ceramic for UO2, has been suggested by molecular dynamics (MD) simulations [6]. Also, the cleavage energy for intergranular fracture in UO2 has been shown to decrease with increasing GB energy [11,12]. The percolation paths for gas release are likely comprised of high energy GBs which favor gas bubble nucleation and growth [13].…”