Oxygen nonstoichiometry and chemical expansion of mixed conducting La0.1Sr0.9Co0.8Fe0.2O3 − δ

The chemical diffusivity and surface exchange constant of La0.1Sr0.9Co0.8Fe0.2O3 − δ (LSCF1982) were successfully extracted by using the chemical expansion relaxation method, and the oxygen nonstoichiometry was determined by electrochemical coulometric titration as a function of oxygen partial pressure (pO2) and temperature. The oxygen chemical diffusivity and surface exchange constants were 3.16 × 10− 4 cm2/s and 6.31 × 10− 3 cm/s at 1000 °C in air, respectively. These values and the activation energies for oxygen diffusion were in good agreement with our own previously reported values determined from the 4-probe D.C. conductivity relaxation method. The oxygen nonstoichiometry was increased with decreasing pO2 and increasing temperature, due to the thermal and chemical release of lattice-site oxygen from the lattice sites. The oxygen self-diffusion coefficient and ionic conductivity were successfully extracted from the relation between the oxygen nonstoichiometry and the chemical diffusion coefficient, and are best expressed by the following equations: D O / cm 2 /s = ( 1.75 ± 0.05 ) × 10 − 4 exp − 0.68 ± 0.10 eV kT | pO 2 = 0.21 atm σ ion T / cm 2 /s K − 1 = ( 4.01 ± 0.02 ) × 10 5 exp − 0.65 ± 0.04 eV kT | pO 2 = 0.21 atm .