The electrical properties of the lanthanum-doped strontium ferrite Sr0.7La0.3FeO3-δ were studied at 750 to 950C and O partial pressures of 10-19 to 0.5atm. The ferrite undergoes a transition from perovskite-like to brownmillerite-like structure at an O pressure of about 10-4atm in the studied temperature range. The observed pressure and temperature dependences of the conductivity in the brownmillerite-like form of the ferrite were related to the transition of the electron conductivity from the intrinsic regime, which was governed by the band gap of about 2eV, to the extrinsic regime, which was controlled by the extra-stoichiometric O in the brownmillerite-like phase. The brownmillerite-like phase was shown to be a mixed conductor with the O conductivity level rising to about 0.3S/cm at about 900C.

High-Temperature Electrical Conductivity of Sr0.7La0.3FeO3-δ. I.A.Leonidov, V.L.Kozhevnikov, M.V.Patrakeev, E.B.Mitberg, K.R.Poeppelmeier: Solid State Ionics, 2001, 144[3-4], 361-9