Cerium effect on the phase stability and redox properties of Ce-doped strontium ferrates

Nanostructured perovskite-type Sr1aCeaFeO3x, (0pao0.15) powders have been prepared by citrate-nitrate smoldering autocombustion. Their phase structure and stability, surface and morphological properties, reduction behavior and interaction with oxygen have been investigated by X-ray Powder Diffraction combined with Rietveld Analysis, 57Fe Mo¨ ssbauer and X-ray Photoelectron Spectroscopies, N2-adsorption method, Temperature Programmed Reduction and Oxidation experiments. Our results reveal that citrate-nitrate auto-combustion method is effective in obtaining single phase Sr1aCeaFeO3x. The Sr1aCeaFeO3x structure is cubic only for aX0.06, while for ao0.06 remains tetragonal. Moreover, for aX0.06 after semi-reductive treatment under inert gas, an expanded cubic phase is obtained instead of the brownmillerite-type structure, which is known to have ordered vacancies. Stabilization of octahedral Fe3+ by cerium doping appears to be the main factor in determining the structural properties of Sr1aCeaFeO3x. The highest oxygen consumption for Ce-doped SrFeO3 occurs for a ¼ 0.06. Preliminary impedance measurements show that Sr0.94Ce0.06FeO3x has the lowest area-specific resistance.