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-delta (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 (pO(2)) and temperature. The oxygen chemical diffusivity and surface exchange constants were 3.16 x 10(-4) cm(2)/s and 6.31 x 10(-3) cm/s at 1000 degrees 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 pO(2) 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-0/cm(2)/s = (1.75 +/- 0.05) x 10(-4) exp (-0.68 +/- 0.10eV/kT)vertical bar(pO2-0.21 atm) sigma T-ion/cm(2)/sK(-1) = (4.01 +/- 0.02) x 10(5) exp (-0.65 +/- 0.04eV/kT)vertical bar(pO2=0.21 atm) (C) 2012 Elsevier B.V. All rights reserved.