Dynamic instability at the origin of oxygen ion conduction in solid oxides at ambient temperature

Pramana

Marie Plazanet²  Tanguy Berthier2¹  Helmut Schober1²  Stefan Eibl²  Mark Johnson²  Olivier Hernandez¹  Monica Ceretti¹  Werner Paulus¹ 

[1] Sciences Chimiques de Rennes, UMR 6226 CNRS Université de Rennes 1, Inorganic Materials: Soft Chemistry and Reactivity of Solids, F-35042 France$$;Institut Laue-Langevin, BP 156 X, F-38042 Grenoble Cedex, France$$

关键词: Neutron inelastic scattering;    diffusion.;   

DOI  :  

学科分类：物理（综合）

来源: Indian Academy of Sciences

【 摘 要 】

The conduction of ions in solids is of paramount importance for many technological devices like solid oxide fuel cells. It is inherent to solids that ions are trapped within potential wells. Their transport thus has to be activated at the price of elevated temperatures, a condition that is often incompatible with technological applications. While atomic vibrations have the potential of assisting the diffusion process, little is known about the exact conditions that have to be reunited to trigger such a process. Here we show that dynamic instability is responsible for the large ion conduction in SrFeO2.5 with brownmillerite-type structure. Using ab-initio molecular dynamics calculations we observe the migration of oxygen ions away from the original lattice positions into the vacancy channels of the brownmillerite structure. The escape of the oxygen ion is rendered possible by the destabilization of a shallow potential well due to low-lying vibrational modes, the existence of which is confirmed by neutron spectroscopy. Analysing the lattice dynamics as a function of structural parameters it is possible to identify the structural subtleties responsible for the instability. It is found that in the isostructural compound CaFeO2.5, fast oxygen ion diffusion is absent at low temperatures. The origin of this behaviour lies with the slightly different iron–oxygen distances rendering the potentials better defined and less amenable to dynamical destabilization. The here-introduced concept of dynamical instability is not restricted to the discussed class of materials but may be applied to any system that features ion conduction at low temperatures.

【 授权许可】

Unknown