Large-scale oxygen order phase transitions and fast ordering kinetics at moderate temperatures in NdNiO electrodes.

Non-stoichiometric 214-nickelates with Ruddlesden-Popper (RP) type frameworks emerged as potential candidates for mixed electronic/ionic conductors in the intermediate temperature range. In this work we investigated structural aspects of the oxygen ion mobility diffusion mechanisms in non-stoichiometric NdNiO nickelates by X-ray (laboratory and synchrotron) as well by neutron diffraction. Temperature dependent synchrotron powder diffraction revealed a phase diagram of unprecedented complexity, involving a series of highly organized, 3D modulated phases related to oxygen ordering below 800 K.

Brownmillerites CaFeO and SrFeO as Catalyst Support for CO Oxidation.

The support material can play an important role in oxidation catalysis, notably for CO oxidation. Here, we study two materials of the Brownmillerite family, CaFeO and SrFeO, as one example of a stoichiometric phase (CaFeO CFO) and one existing in different modifications (SrFeO, SrFeO and SrFeO, SFO). The two materials are synthesized using two synthesis methods, one bottom-up approach via a complexation route and one top-down method (electric arc fusion), allowing to study the impact of the specific surface area on the oxygen mobility and catalytic performance.

Determination of the magnetic structures in orthoferrite CeFeOby neutron powder diffraction: first order spin reorientation and appearance of an ordered Ce-moment.

High resolution and high intensity neutron powder diffraction are used to determine the temperature dependence of the crystallographic and magnetic structure of the orthoferrite CeFeO. The high temperature-type magnetic coupling of the Fe-sublattice described by the Γ() irreducible representation changes at the spin reorientation temperature= 228 K to a-type coupling of Γ(). The spin reorientation is of first order and sees a hysteresis of about 2.

Local Structures of Oxygen-Deficient Perovskite SrScGaO Polymorphs Explored by Total Neutron Scattering and EXAFS Spectroscopy.

Depending on the synthesis route, the oxygen ion electrolyte SrScGaO shows two polymorphs, a brownmillerite and a cubic perovskite framework. In order to better explore oxygen diffusion pathways and mechanisms, we report here on a multitechnical approach to characterize local structural changes for SrScGaO polymorphs as a function of temperature, using a neutron pair distribution function (PDF) analysis together with an extended X-ray absorption fine structure (EXAFS) analysis. While for the brownmillerite type structure PDF and Rietveld refinements yield identical structural descriptions, considerable differences are found for the cubic oxygen-deficient polymorph.

(Nd/Pr)NiO: Reaction Intermediates and Redox Behavior Explored by in Situ Neutron Powder Diffraction during Electrochemical Oxygen Intercalation.

Oxygen intercalation/deintercalation in PrNiO and NdNiO was followed by in situ neutron powder diffraction during electrochemical oxidation/reduction, in a dedicated reaction cell at room temperature. For both systems three phases, all showing the same line width, were identified. The starting phases PrNiO and NdNiO, considered with an average orthorhombic Fmmm symmetry, although both show a slight monoclinic distortion, get reduced in a two-phase reaction step to tetragonal intermediate phases with 0.