The effect of impurities on vacancy migration at NiO grain boundaries

Diffusion within ceramics is an important mechanism for the growth of oxide films. Experiments show that the addition of impurities can drastically re duce the rate at which the film grows. This, the reactive element effect, i s very useful for corrosion protection. Grain boundaries are regions of hig h diffusivity and high defect concentration and are important for studying this effect. We present the results of atomistic simulations, using a modif ied molecular dynamics method, to calculate the effect of neutral impuritie s upon the activation energies and diffusion pathways of vacancy migration at {310} and {410} tilt grain boundaries of NiO. We show that there is a co rrelation between the size of the impurity ion and its favoured position wi thin the boundary. The presence of impurities increases the activation ener gies and diffusion pathways to a greater extent for the (310) boundary than for the {410} boundary.