Coulometric titration techniques were used to measure chemical diffusion at temperatures of between 700 and 1000C. The transient current response to a potentiostatic step was transformed from the time domain to the frequency domain. The equivalent circuit which was used to fit the resultant impedance data contained an element which described the finite-length diffusion of O into the sample. Other elements which were included were the gas-phase capacitance, and the sum of the gas-phase diffusion resistance and that which was associated with the limited surface exchange kinetics of the sample. The chemical diffusion coefficient of the perovskite, La0.8Sr0.2CoO3, was determined as a function of temperature and O partial pressure. It could be described by:

D(cm2/s) = 5.91 exp[-135(kJ/mol)/RT]

and was essentially independent of O partial pressures ranging from 0.01 to 0.209bar.

M.H.R.Lankhorst, H.J.M.Bouwmeester: Journal of the Electrochemical Society, 1997, 144[4], 1261-8