Mass and charge transport properties of La0.9Ca0.1FeO3 − δ

The mixed ionic electronic conducting perovskite La0.9Ca0.1FeO3 − δ (LCF91) was synthesized via a glycine-nitrate process. XRD measurements and Rietveld analysis showed LCF91 as the main phase and a minor amount of brownmillerite Ca2Fe2O5 as secondary phase. The oxygen exchange kinetics and the electronic conductivity of LCF91 were determined as functions of the oxygen partial pressure (1 × 10− 3 ≤ pO2/bar ≤ 0.1) and temperature (600 ≤ T/°C ≤ 800). The chemical surface exchange coefficient kchem and the chemical diffusion coefficient of oxygen Dchem were obtained from in-situ dc-conductivity relaxation experiments. High values of kchem = 9 × 10− 4 cm s− 1 and Dchem = 7 × 10− 6 cm2 s− 1 were obtained at 800 °C and pO2 = 0.01 bar. The activation energies for kchem and Dchem were in the range of 33 ≤ Ea/kJ mol− 1 ≤ 43 and 61 ≤ Ea/kJ mol− 1 ≤ 67, respectively. The oxygen nonstoichiometry of LCF91 was described by a point defect model to obtain the concentrations of electronic and ionic defects as a function of pO2 and temperature. Based on the defect model, the thermodynamic factors of oxygen and oxygen vacancies were determined. Self-diffusion coefficients for oxygen and oxygen vacancies were estimated to 1.3 × 10− 9 ≤ DO/cm2 s− 1 ≤ 1.2 × 10− 8 and 6.3 × 10− 7 ≤ DV/cm2 s− 1 ≤ 2.5 × 10− 6 at 700-800 °C, respectively. The electronic and ionic conductivities were in the range of 28 ≤ σe/S cm− 1 ≤ 35 (600-800 °C) and 5.7 × 10− 6 ≤ σi/S cm− 1 ≤ 4.9 × 10− 4 (700-800 °C), respectively.