A simple method for the determination of surface exchange and ionic transport kinetics in oxides

A method is proposed for obtaining the surface exchange coefficient (k) and chemical diffusion coefficient (D) for oxide materials under reducing conditions. Transient oxygen stoichiometry re-equilibration data is obtained from powdered samples using solid electrolyte coulometry where oxygen dosing/titration is performed by means of electrochemical cells. The data has been fitted to a suitable diffusion model using a non-linear parameter optimisation method from which the parameter k and D have been extracted. This method has been applied to the perovskite material La0.6Sr0.4Co0.2Fe0.8O3-delta at intermediate temperatures and reduced oxygen pressures in the range 1 x 10(-3) -6.3 X 10(-5) atm. The results obtained in this study were found to be consistent with those obtained by means of other relaxation techniques. (C) 2000 Elsevier Science B.V. All rights reserved.