A new oxide of the Ruddlesden-Popper series has been isolated and structurally characterized in the Eu-Sr-Co-Mn-O system. X-ray diffraction and electron microscopy show that polycrystalline Eu 2 SrCo 1.5 Mn 0.5 O 7 constitutes the n=2 member of a homologous series, the essential feature of which is the existence of two connected Co/Mn octahedral layers, separated by Eu atoms. Electrochemical study shows that, the area-specific resistance of this compound is 0.15Ω cm 2 at 700 ºC in air, a performance which is comparable to that of the best state-of-the-art materials used as cathode in intermediate temperature solid oxide fuel cells. Below 150 K the title material presents two different magnetic phenomena. The first one corresponds to the formation of ferromagnetic nanoclusters (T C ∼121 K) within an ordered Co 2+ /Mn 4+ atomic configuration, whereas at lower temperature (∼21 K) a spin glass state occurs. Figure 3. (a) HAADF image of along Eu 2 SrCo 1.5 Mn 0.5 O 7 [0 1 0]. A schematic model for cationic position has been inserted. (b) Corresponding ABF image where cationic atoms are in red and oxygen are in blue. Interstitial oxygen ions are indicated by blue arrows. a along [110] pseudocubic axis in a given two-layer perovskite block and along [-110] direction in adjacent blocks. Physical Properties Magnetic behaviour.The magnetic behaviour of oxides is related to metal oxidation states, charge localization and ordering phenomena, which are also related with transport properties. Thus, magnetic measurements may help to understand the electrical properties of a given material.

New oxides of the (NdSr)MO (M = Co and Mn or Fe) series are reported. Compounds of composition NdSrCoFeO, NdSrCoMnO and NdSrCoMnO are the n = 1 members of the Ruddlesden-Popper homologous series (KNiF structural type) as determined by X-ray diffraction and different transmission electron microscopy techniques. Their crystal structure consists of connected (Co-Fe/Mn)O octahedra blocks separated by (Nd/Sr)O rock-salt like layers along the c-axis. Interstitial oxygen atoms or anion vacancies are induced depending on composition. Oxides with interstitial oxygen show good performances as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. The area-specific resistance values of electrodes made of these oxides at 973 K in air are 0.18 Ω cm for NdSrCoFeO and NdSrCoMnO (comparable to the one of the state-of-the-art materials proposed as cathodes in IT-SOFC), and 1.38 Ω cm for NdSrCoMnO.

A solid solution of Nd 1-x Sr x CoO 3-δ (with x=0, 1/3, 2/3, and 1) has been prepared and characterized by a combination of X-ray diffraction, electron microscopy, and electron energy-loss spectroscopy (EELS). The structural characterization indicates that Nd-doped materials present an orthorhombic symmetry with a=√2xa p, b=√2xa p, and c=2xa p (a p refers to lattice parameter of simple cubic perovskite), while SrCoO2.5 has an orthorhombic symmetry with a=√2xa p, b=4xa p, and c=√2xa p. EELS analysis revealed that Co are in 3+ oxidation states but in different spin configurations.