High-temperature electrical transport in La0.3Sr0.7Fe1-xGaxO3-x (x=0-0.5)

The electrical properties of perovskite-related oxide La0.3Sr0.7Fe1-xGaxO3-delta (x = 0-0.5) are reported within the temperature range 750 to 950 degreesC and the oxygen partial pressure range between 10(-19) and 0.5 atm. The maximum solid solubility of gallium in the iron sublattice of La0.3Sr0.7FeO3-delta 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 degreesC. Ionic conduction in the vacancy ordered phases decreases with increasing gallium concentration.