Optical investigation of oxygen incorporation in SrTiO 3

Abstract

An optical method for the study of oxidation kinetics in SrTiO 3 is presented. A controlled amount of Fe impurities which is important to define the defect-chemistry with respect to unknown impurity background effects, also gives rise to the possibility of detecting the oxygen uptake/removal by in situ absorption spectroscopy. In this way the kinetics is shown to be diffusion limited at high temperatures (and large sample thicknesses) and to be surface-reaction limited at low temperatures (and low sample thicknesses). It is moreover shown that in the case of trapping effects the chemical diffusion coefficient cannot be analysed according to the conventional theory of chemical diffusion. The correct study results in the surprising fact, that the chemical diffusion coefficient can, due to trapping effect, be even lower than both the diffusivity of the decisive-mobile-ionic and the decisive-mobile-electronic carrier. The analysis also shows that the evaluation of the relaxation behaviour of different species during a stoichiometric relaxation does not necessarily lead to the same effective diffusion coefficients.