Defect chemical analysis of the electronic conductivity of strontium-substituted lanthanum ferrite

The electronic conductivity of La0.4Sr0.6FeO3−δ is studied in the oxygen partial pressure range 10−5≤pO2/atm≤1 at temperatures 100≤T/°C≤900. The oxygen partial pressure dependence of the electronic conductivity in the pO2 range under investigation shows a predominantly p-type character. Combination of the pO2 dependences of the oxygen nonstoichiometry δ and the electronic conductivity σ at constant temperatures 600≤T/°C≤900 indicates a significant decrease of σ with increasing δ. Concentrations of electronic defects are calculated from experimental data of the oxygen nonstoichiometry via a point defect model and applied to modelling of σ as a function of δ. The mobility of holes is estimated from the electronic conductivity and the calculated charge carrier concentrations as a function of oxygen nonstoichiometry. At constant pO2, the electronic conductivity is thermally activated at T<300 °C, but decreases with further increase of temperature due to desorption of oxygen from the lattice. This effect is especially pronounced in the intermediate pO2 range 10−4≤pO2/atm≤10−2 where significant oxygen deficit occurs. The temperature dependence of the electronic conductivity of La0.4Sr0.6FeO3−δ was combined with results of the temperature dependence of the oxygen nonstoichiometry. Thus, activation energies for electronic conduction at constant oxygen content were obtained for the high temperature region (T>300 °C) which are in agreement with isobaric activation energies of the electronic conductivity at low temperatures (T<300 °C).