Measurement of chemical diffusion coefficient and surface exchange on mixed ionic electronic conductors using periodical pO2 oscillations

It was shown that the conductivity relaxation method combined with pO2 oscillations is a very good tool to estimate the material related transport parameters. The obtained diffusion and surface exchange coefficients are equivalent to the tracer diffusion coefficients and surface rate constant of oxygen defects respectively. These coefficients are independent on the defect concentration and can be used as general constants for the estimation ofthe ionic conductivity and the polarization resistance of the materials at given oxygen partial pressure if the concentration of mobile anion species is known (i.e. previously measured by thermogravimetry). In comparison to the standard conductivity relaxation principle, the main advantages of this method are the independence of the sample thickness (for the simultaneous measurement of D and k) and the insensitivity to the delta-pO2 dependence. However the dependence sigma-pO2 should be well known for the applied pO2-range and is essent ial for FEM (finite element method) calculations. Due to the very high precision of the measured data in the different frequency ranges, the precision of D and k calculations using the developed FEM simulation is rather high. To obtain the oxygen tracer diffusion coefficients the concentration of the defects at the desired temperature and oxygen partial pressure should be additionally measured (pO2-T-delta characteristics) or calculated. The comparison of the obtained results to the data from the literature shows a very good agreement.