Advances in point defect chemistry: space charge controlled surface reactions

A theoretical point defect model for the transition between two equilibrium states is proposed. Material constants are taken from lanthanum-doped SrTiO3, which serves as a model material for donor-doped perovskites. A finite-differences method is used to compute the time dependent evolution of defect concentrations after an excitation of the system. For the calculation of the particle fluxes of all charged defects, time variant surface concentrations of all mobile species are considered via local defect equilibria. As the surface concentrations differ significantly from the new equilibrium values, a drastic change of the electrical properties in the near-surface region is expected. The new approach is strongly supported by the resistivity change of the material in an oxidation experiment. A comparison between simulation and experimental data confirms the excellent applicability of the model.