Abstract

The electrical properties of perovskite-related oxide La_0.3Sr_0.7Fe_1 - xGa_xO_3 − δ (x = 0–0.5) are reported within the temperature range 750 to 950 °C and the oxygen partial pressure range between 10⁻¹⁹ and 0.5 atm. The maximum solid solubility of gallium in the iron sublattice of La_0.3Sr_0.7FeO_3 − δ is close to 30%. At oxygen pressures about 10⁻⁴ atm, the materials undergo a transition from perovskite to oxygen vacancy ordered structures. The type of vacancy ordering depends on gallium content. Both p- and n-type electronic conductivities decrease when insulating gallium cations having stable oxidation state are incorporated into the iron sublattice of the ferrite. The observed temperature and oxygen pressure dependencies of the p-type electronic conductivity in the ordered phases suggest a transition from the intrinsic regime, when the electron–hole conduction is governed by the band gap, to the extrinsic regime, controlled by the amount of the oxygen excess in the vacancy ordered structure. The ordered strontium–lanthanum ferrite was shown to be a mixed conductor with oxygen ionic conductivity of about 0.1 S cm⁻¹ at 900 °C. Ionic conduction in the vacancy ordered phases decreases with increasing gallium concentration.