Abstract
Ca2Fe0.5Ga1.5O5 is an oxygen-deficient perovskite, where the defects generated due to oxygen-deficiency are distributed in an ordered fashion. Neutron diffraction experiments indicate that the defect-order results in the formation of alternating (Ga)O4 tetrahedral and (FeGa)O6 octahedral units, forming the so-called brownmillerite-type structure. This material represents the highest degree of Ga-doping in the brownmillerite compound Ca2Fe2O5, which can be achieved using solid-state synthesis method. X-ray photoelectron spectroscopy (XPS) combined with iodometric titration was employed to determine the Fe oxidation state and the oxygen-content in Ca2Fe0.5Ga1.5O5. The XPS studies show that Fe is predominantly in trivalent state, and the iodometric titrations indicate that the oxygen stoichiometry is 5.07 per formula unit, consistent with primarily trivalent Fe. Variable-temperature electrical conductivity studies of Ca2Fe0.5Ga1.5O5 have been performed in a wide temperature range, 25–800 °C, indicating semiconducting behavior and significant contribution of ionic conductivity to total conductivity of this material.
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