Oxygen nonstoichiometry and chemical expansion of mixed conducting La _(0.1)Sr _(0.9)Co _(0.8)Fe _(0.2)O _(3 - δ)

摘要

The chemical diffusivity and surface exchange constant of La _(0.1)Sr _(0.9)Co _(0.8)Fe _(0.2)O _(3 - 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 (pO _2) and temperature. The oxygen chemical diffusivity and surface exchange constants were 3.16 × 10 ~(- 4) cm ~2/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 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 _O/cm ~2/s=(1.75±0.05)×10 ~(-4)exp-(-0. 68±0.10eV/kT)| _(pO2=0.21atm)σ _(ion)T/cm ~2/sK ~(-1)=(4.01±0.02)×10 ~5exp-(-0. 65±0.04eV/kT)| pO2=0.21atm.