Measurement of Transport Properties by Conductivity Relaxation on Dense La0.6Sr0.4CoO3 − δ With and Without Porous Surface Layers

Abstract

Conductivity relaxation experiments were conducted on (LSC40) over a temperature range from 600 to and oxygen partial pressure, , switch from 0.21 to in atmospheres. Two types of samples were used: One was a bar-shaped dense sample of thickness with polished surfaces. The other was an identical sample but with porous surface layers of LSC40, which were applied to enhance kinetics of the surface exchange process. It was observed that the kinetics of conductivity relaxation in the sample with porous layers was much faster than in the sample without porous layers, and data fitting on the sample with porous surface layers was only sensitive to the chemical diffusion coefficient, , but not to the surface exchange process. Using estimated from the sample with porous layers, the chemical surface exchange coefficient, , was determined from conductivity relaxation data on the sample without porous layers. These and are presumed to be accurate values of the parameters for the material under the measurement conditions (temperature and ). It was observed that fitting the conductivity relaxation data on the sample without porous layers by simultaneously varying and , however, led to significant uncertainties in both of the estimated parameters. In general, fitting the data obtained on the polished sample to and simultaneously led to an overestimation of and underestimation of . The present work also shows that the measured is expected to be substantially affected by the surface preparation procedure used.