Combining Multiscale Approaches for the Structure Determination of an Iron Layered Oxysulfate: Sr₄Fe_2.5O_7.25(SO₄)_0.5

The new iron layered oxysulfate Sr₄Fe_2.5O_7.25(SO₄)_0.5 has been prepared by a solid-state reaction in closed ampules into the form of ceramics and single crystals. Its atomic structure has been solved by means of spectroscopy, diffraction techniques, and high-resolution electron microscopy. Sr₄Fe_2.5O_7.25(SO₄)_0.5 is a layered structure that derives from the Ruddelsden–Popper (RP) phases with the layer stacking sequence SrO/SrFeO_2.5/SrFe_0.5(SO₄)_0.5O_1.25/SrFeO_2.5. Within the mixed Fe³⁺/SO₄^2– layer, the sulfur atoms are slightly shifted from the B site of the perovskite and each sulfate group shares two corners with iron pyramids in the basal plan without any order phenomenon. The electronic conductivity is thermally activated, while no ionic conductivity is detected

Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO₃ perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO₃ network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO₃ network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation