Determination of oxygen nonstoichiometry and diffusivity in mixed conducting oxides by oxygen coulometric titration .1. Chemical diffusion in La0.8Sr0.2CoO3-delta

Oxygen coulometric titration has been applied to measure chemical diffusion in La0.8Sr0.2CoO3-delta between 700 and 1000 degrees 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 La0.8Sr0.2CoO3-delta oxygen partial pressure. Its value can be represented by (D) over cap (cm(2)/s)=5.91 x exp [(-135 kJ/mol)/RT], and turns out to be practically independent of oxygen partial pressure in the range 10(-2) -0.209 bar.