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 degr eesC and the oxygen partial pressure range between 10(-19) and 0.5 atm. The maximum solid solubility of gallium in the iron sublattice of La0.3Sr0.7Fe O3-delta is close to 30%. At oxygen pressures about 10(-4) atm, the materia ls undergo a transition from perovskite to oxygen vacancy ordered structure s. The type of vacancy ordering depends on gallium content. Both p- and n-t ype electronic conductivities decrease when insulating gallium cations havi ng 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 fr om the intrinsic regime, when the electron-hole conduction is governed by t he band gap, to the extrinsic regime, controlled by the amount of the oxyge n 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 ordere d phases decreases with increasing gallium concentration.