Determination of Oxygen Nonstoichiometry and Diffusivity in Mixed Conducting Oxides by Oxygen Coulometric Titration: I. Chemical Diffusion in

Oxygen coulometric titration has been applied to measure chemical diffusion in between 700 and 1000°C. The transient current response to a potentiostatic step has been transformed from the time domain to the frequency domain. The equivalent circuit used to fit the resulting impedance data contains the element that describes the finite‐length diffusion of oxygen into the sample specimen. Other elements included are the gas‐phase capacitance and the sum of the gas‐phase diffusion resistance and that associated with the limited surface exchange kinetics of the sample. The chemical diffusion coefficient of perovskite has been determined as a function of temperature and oxygen partial pressure. Its value can be represented by (cm 2 /s) = 5.91 × exp [(−135 kJ/mol)/ RT ], and turns out to be practically independent of oxygen partial pressure in the range .