Hydrogen in Zirconium: Atomistic Simulations of Diffusion and Interaction with Defects using a New Embedded Atom Method Potential
Erich Wimmer, Mikael Christensen, Walter Wolf, W. H. Howland, B. Kammenzind, R. W. Smith
Journal of Nuclear Materials
A new interatomic embedded atom method (EAM) potential, called BMD19, has been developed for simulations of hexagonal zirconium with dissolved hydrogen. The parameters are fitted to data from density functional calculations and calibrated using the experimental room-temperature density of zirconium. The new potential overcomes the unphysical negative thermal expansion coefficient between 0 and 200 K obtained with the frequently used Mendelev-Ackland potential (MA#3). It reproduces the geometry around self-interstitial atoms (SIA’s) obtained with DFT while the MA#3 and the COMB3 potentials yield structures with the SIA between basal planes.
The energies of forming vacancies and self-interstitials as well as the elastic coefficients are of similar quality for all potentials investigated in the present work. Compared with DFT results, the new potential describes the interactions of H with Zr better overall than any previously published interatomic potentials. This includes the binding energy of interstitial H and its dependence on lattice strain for tetrahedral and octahedral sites, the trapping energy in vacancies, surface segregation energy, and the energy of diffusion barriers. The present work illustrates the usefulness of the BMD19 potential by showing the dependence of diffusion coefficients on lattice strain, the accumulation of H in vacancy c-loops and by correctly describing the Soret effect, i.e. the diffusion of H from hotter to colder regions of the material. Simulations of the effect of grain boundaries and internal surfaces (e.g. nano-voids) and diffusion on surfaces provide further demonstrations of the usefulness of this new potential.