Surface and redox chemistry of Sm0.95Ce0.05Fe1 − xNixO3 − δ perovskites

A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has been prepared by sol–gel combustion via a citrate precursor route. X-ray diffraction data showed that materials prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. The study of powders sintered in air and in reducing atmospheres reveals that these materials do not show phase separation in air (up to 1350 °C) nor under 5% v/v H2/N2 (up to 700 °C), but a phase separation of Sm2O3 does occur at and above 800 °C under 5% v/v H2/N2 without deterioration of the perovskite phase. The surfaces of all the powders (fresh, in-situ reduced and ex-situ reduced) were Sm rich, and multiple oxidation states for Fe were observed. XP analysis of in-situ reduced samples (800 °C and above) shows that metallic Fe forms in all nickel doped materials except x = 0.07. The surface oxygen vacancies and percentages of lattice and adsorbed oxygen for this series of Ni doped materials were determined and the oxygen recapturing ability is explained in terms of the multiple oxidation states of Fe.