Structural Chemistry & Crystallography Communication

STRUCTURAL FEATURES OF A NEW OXYGEN DEFICIENT PEROVSKITE SR2SCGAO5, A PROMISING OXYGEN ION CONDUCTOR AT MODERATE TEMPERATURE

3^rd Edition of International Conference on Advanced Spectroscopy, Crystallography and Applications in Modern Chemistry
June 04-05, 2018 London, UK

Monica Ceretti

Institut Charles Gerhardt Montpellier, France

Keynote: Struct Chem Crystallogr Commun

DOI: 10.21767/2470-9905-C1-004

Abstract

Oxygen ion conductors are materials of major interest for a series of application in the area of solid state ionics (fuel cells, batteries, electrodes, sensors, catalysts, etc…). In this respect oxides with brownmillerite type structure (A2BB’O5), have attracted much attention, especially as they show oxygen ion mobility down to ambient temperature. This mobility is a result of a phonon assisted diffusion mechanism, based on a dynamic oxygen disorder scenario of the infinite BO4 chains [1, 2]. Brownmillerite type frameworks containing B-cations with saturated or empty electron shells (d0 or d10 configurations) present a special case, as they impose a fixed oxygen stoichiometry, making them good candidates to study oxygen diffusion mechanisms on a microscopic level. In this context, we have synthesized a new phase Sr2ScGaO5, having pure oxygen ion conductivity. Depending on the synthesis route, it shows two polymorphs: orthorhombic Brownmillerite type structure or an oxygen deficient cubic perovskite structure. When synthesizing Sr2ScGaO5 by classical solid state reaction at 1200°C, the thermodynamically stable phase obtained shows the brownmillerite framework [3]. Heating at higher temperature, it shows a phase transition to the cubic perovskite structure completed at 1500°C, associated with improved oxygen ion conduction [4]. Since the cubic symmetry can be maintained down to ambient temperature, we were able to grow high quality single crystal of the cubic phase [5]. We report here on a combination of characterization on the brownmillerite as well on the cubic Sr2ScGaO5. High-resolution structure analysis has been performed using X-rays (synchrotron and laboratory) and neutron diffraction methods, combined with NMR analysis for local environment [3]. In particular, single crystal neutron diffraction with subsequent analysis of the nuclear scattering density by the Maximum Entropy Method has been performed
in order to describe in more detail oxygen displacement factors and associated diffusion pathways [5]. To better understand the oxygen mobility mechanisms, these studies were complemented by Raman and impedance spectroscopy.
Recent Publications 1. Paulus W. et al. (2008) Lattice Dynamics To Trigger Low Temperature Oxygen Mobility in Solid Oxide Ion Conductors. Journal of the American Chemical Society, 130(47): p. 16080-16085. 2. Ceretti M. et al. (2015) Low temperature oxygen diffusion mechanisms in Nd2NiO4+ and Pr2NiO4+ via large anharmonic displacements, explored by single crystal neutron diffraction. Journal of Materials Chemistry A, 3(42): p. 21140-21148. 3. Corallini S. et al.. (2015) One-Dimensional Oxygen Diffusion Mechanism in Sr2ScGaO5 Electrolyte Explored by Neutron and Synchrotron Diffraction, 17O NMR, and Density Functional Theory Calculations. The Journal of Physical Chemistry C, 119(21): p. 1144711458. 4. Ceretti M. et al. (2016) Influence of Phase Transformations on Crystal Growth of Stoichiometric Brownmillerite Oxides: Sr2ScGaO5 and Ca2Fe2O5. Crystals, 6(11): p. 146.
5. 5. Corallini S. et al. (2017) Cubic Sr2ScGaO5 Perovskite: Structural Stability, Oxygen Defect Structure, and Ion Conductivity Explored on Single Crystals. Inorganic Chemistry, 56(5): p. 2977-2984.
 

Biography

Monica Ceretti has an experitse in neutron diffraction for crystal structural studies. After 14 years at the Laboratoire Léon Brillouin (Saclay, France) as scientific responsible of a neutron diffractometer, she first moved to the University of Rennes and then in Montpellier (chemistry department), where she is in charge for structural studies of correlated oxides by neutron and X-ray diffraction. Member of several panels for proposals review at large scale facilities (at the ILL in the past and now at FRM2) in the crystallography committees, she is involved in training activities in neutron scattering for structural studies in the frame of master courses as well as in specialized schools.
Email:monica.ceretti@umontpellier.fr