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

Abstract

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^δ is derived from the concept of conservative ensembles for two independent trapping reactions. Finite difference simulations show that the stoichiometry dependence of D^δ 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^δ occurs in the outer sample region.