Reactive force field simulation of proton diffusion inBaZrO3 using an empirical valence bond approach

Abstract

A new reactive force field to describe proton diffusion within the solid oxide fuel cell materialBaZrO3 has been derived. Using a quantum mechanical potential energy surface, the parameters of aninteratomic potential model to describe hydroxyl groups within both pure and yttrium-dopedBaZrO3 have been determined. Reactivity is then incorporated through the use of the empiricalvalence bond model. Molecular dynamics simulations (EVB-MD) have been performed toexplore the diffusion of hydrogen using a stochastic thermostat and barostatwhose equations are extended to the isostress–isothermal ensemble. In the lowconcentration limit, the presence of yttrium is found not to significantly influence thediffusivity of hydrogen, despite the proton having a longer residence time at oxygenadjacent to the dopant. This lack of influence is due to the fact that trappingoccurs infrequently, even when the proton diffuses through octahedra adjacent tothe dopant. The activation energy for diffusion is found to be 0.42 eV, in goodagreement with experimental values, though the prefactor is slightly underestimated.