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:DO/cm2/s=(1.75±0.05)×10−4exp−0.68±0.10eVkT|pO2=0.21atmσionT/cm2/sK−1=(4.01±0.02)×105exp−0.65±0.04eVkT|pO2=0.21atm.

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► The chemical diffusivity and surface exchange constant of La0.1Sr0.9Co0.8Fe0.2O3 − δ
► The oxygen nonstoichiometry by electrochemical coulometric titration
► Partial molar enthalpy and entropy of oxygen from stoichiometric oxygen partial pressure
► The oxygen ion conductivity extracted by solving the Nernst–Einstein