Syntheses and Crystal Structures of the First Bromofluorides in Niobium Cluster Chemistry: Nb6Br8F7 and Na2NbF6–(Nb6Br4F11)

The electrical properties of the strontium ferrite are reported within the temperature range 700 to 950°C and the oxygen partial pressure range between 10-18 and 0.3 atm. The observed pressure and temperature dependencies of the conductivity in the brownmillerite form of the ferrite are related to the transition of the electron conductivity from the intrinsic regime, which is governed by the band gap of about 2 eV, to the extrinsic regime, which is controlled by the extrastoichiometric oxygen in the brownmillerite phase. The brownmillerite phase is shown to be a mixed conductor with the oxygen conductivity rising to about 0.1 S/cm at 850–900°C and po2 >10-17 atm. The perovskite-like layers in the brownmillerite structure provide a possible pathway for the ion migration.