AN OPTICAL IN-SITU METHOD TO STUDY REDOX-KINETICS IN SRTIO3

The optical absorption properties of Fe-impurity centers in SrTiO3 can be used to probe-in-situ the oxygen activity in the sample. The response of the absorbance upon a sudden change the oxygen partial pressure allows the precise investigation of the kinetics of oxygen incorporation (excorporation). In contrast to electrical measurements no auxiliary contact phases (electrodes) are necessary and also - as shown - valence changes of the impurity ion do not complicate the evaluation. The investigations indicate a change from diffusion control to surface control when lowering the temperature or decreasing the sample thickness. Effective rate constants and chemical diffusion coefficients are determined. It is shown that the chemical diffusion coefficient cannot be understood in terms of charge carrier mobilities and concentrations unless the effect of internal defect-chemical reactions (here valence changes of the Fe-ions) is taken into account as previously described by one of us. Using this approach, however, the values can be quantitatively described without any adjustable parameter.