Chemical diffusion with non-constant Dδ and the appearance of a parabolic rate law:: Model study on SrTiO3

The chemical diffusion of oxygen in Fe-doped SrTiO3 single crystals driven by large changes in the ambient oxygen partial pressure p(o2), is Studied. The stoichiometry dependence of the chemical diffusion coefficient D-delta is derived from the concept of conservative ensembles for two independent trapping reactions. Finite difference simulations show that the stoichiometry dependence of D-delta can lead to the appearance of a parabolic rate law (which typically applies to two- or multiple-phase systems) even in single-phase systems, provided a strong increase of D-delta occurs in the outer sample region.