Nanoscale Ordering in Oxygen Deficient Quintuple Perovskite Sm_2-εBa_3+εFe₅O_15-δ: Implication for Magnetism and Oxygen Stoichiometry

The investigation of the system Sm–Ba–Fe-O in air has allowed an oxygen deficient perovskite Sm 2-ε Ba 3+ε Fe 5 O 15-δ (δ = 0.75, ε = 0.125) to be synthesized. In contrast to the XRPD pattern which gives a cubic symmetry ( a p = 3.934 Å), the combined HREM/EELS study shows that this phase is nanoscale ordered with a quintuple tetragonal cell, “ a p × a p × 5a p ”. The nanodomains exhibit a unique stacking sequence of the A-site cationic layers along the crystallographic c -axis, namely “Sm–Ba–Ba/Sm–Ba/Sm–Ba–Sm”, and are chemically twinned in the three crystallographic directions. The nanoscale ordering of this perovskite explains its peculiar magnetic properties on the basis of antiferromagnetic interactions with spin blockade at the boundary between the nanodomains. The variation of electrical conductivity and oxygen content of this oxide versus temperature suggest potential SOFC applications. They may be related to the particular distribution of oxygen vacancies in the lattice and to the 3d 5 L configuration of iron.