Experimental and numerical assessment of grain boundary energies in polycrystalline uranium dioxide

Uranium dioxide ceramics are widely used as nuclear fuels. Thus, it is important to understand the role of the grain boundaries (GBs) which decisively govern the properties of these polycrystalline materials and subsequently determine their performances. Here, we report a coupled numerical - experimental approach enabling to assess GB energies. Firstly, GB formation energies (γ_gb) were computed for 34 symmetric tilt GBs in UO₂ with molecular dynamics simulations at 1700 K. The surface energies (γ_S) relative to the respective planes of these GBs were calculated as well. The Herring relation was then used to assess the dihedral angles Ψ of the corresponding GB grooves. Secondly, a UO₂ ceramic sample was annealed at 1673 K to obtain GB grooves. The CSL GBs of interest were identified by EBSD and their Ψ angles determined by AFM. Computed and measured Ψ values were found to be very close.