A first principles study of zirconium grain boundaries

We present the results of first-principles calculations of selected structural and thermodynamic properties of a set of grain boundaries (GBs) in zirconium, spanning a range of misorientation angles and boundary planes. We performed plane-wave density functional theory calculations on low-Σ grain boundaries — five symmetric tilt GBs (STGBs) and three twist GBs; all with misorientation axes about [0 0 0 1] and in optimised microscopic configurations — to gain insight into the associated atomistic structures. We include in our analysis properties such as GB excess volume, interplanar spacing, volume per atom, electron density distribution, and a measure of GB width. We found the twist GBs to exhibit similar energetic and structural properties, whereas the STGBs showed substantially more variation. Our comprehensive analysis demonstrates how all five dimensions of GB space are crucial in determining properties such as the work of ideal separation and the length scale over which atoms are perturbed by the presence of the GB. Additionally, we compared our first-principles results to predictions from a widely used embedded-atom method (EAM) potential; we found the potential to perform generally well, particularly in predicting GB energy. We discuss the results in terms of representing the initial steps towards the development of a mechanistic understanding of the pellet-cladding interaction in nuclear fuel, which must involve encoding accurate materials behaviour at larger length and time scales. To this end, and so that our results can be useful for further investigations, we have published our data (including optimised structures, computed interface energetics and structural properties) to a public repository.