Lattice Dynamics Modified by Excess Oxygen in Nd₂NiO_4+δ: Triggering Low-Temperature Oxygen Diffusion

Abstract

Low temperature, oxygen diffusion, lattice dynamics, Nd 2 NiO 4+δ , molecular dynamics, non stoichiometric oxides, inelastic neutron scattering ABSTRACT. Non-stoichiometric Nd 2 NiO 4+δ shows oxygen ion mobility already at roomtemperature, and as such is a promising materials in the field of solid state ionic conductors. The present work aims to understand the impact of oxygen over-stoichiometry on the lattice dynamics of the Nd 2 NiO 4 framework, and to correlate dynamic instabilities to the anionic mobility at room temperature. We performed neutron time-of-flight spectroscopy experiments coupled with DFT based molecular dynamics calculations on the phases Nd 2 NiO 4.0 , Nd 2 NiO 4.10

Kinetics of Oxygen Surface Exchange on Epitaxial Ruddlesden–Popper Phases and Correlations to First-Principles Descriptors

“…[13][14] Although the origin of the phonon-assisted diffusion is different from the classical push-pull mechanism activated at higher temperatures, both oxygen transport mechanisms are coupled to, or mediated by, oxygen interstitials in the undoped RP 214 phases. 13,15 Overall, these results indicate that despite structural similarity, much greater complexity occurs in the RP 214 systems than the perovskite materials, due to coupling and interplay between material anisotropy, bulk defect chemistry, and lattice dynamics, which have either direct or indirect influences on their bulk oxygen transport and oxygen surface exchange kinetics.…”

Inelastic neutron scattering applied to materials for energy

“…In the following a couple of examples will be presented in which recently inelastic neutron experiment have helped understanding material properties on systems less prone to profit of the neutron characteristic as oxygen ion conductors [6] and thermoelectric materials [7].…”

Exploring local disorder in fast oxygen ion conductors by atomic pair distribution function analysis

“…This then easily leads to a push pull mechanism as described for La 2 NiO 4+ [6] above 800 K in the tetragonal phase, as well as for (Pr/Nd) 2 NiO 4+ [7]. Recent studies, based on a combination of inelastic neutron scattering together with DFT-based Molecular Dynamics simulations and analyzed by a new developed position recurrence method, clearly evidenced for Nd 2 NiO 4+ that oxygen mobility is activated dynamically as low as ambient temperature [2] allowing exchange between the apical and interstitial oxygen positions on a ps time scale. It becomes thus clear that specific lattice dynamics and related oxygen displacements from their equilibrium positions are a key issue to understand the diffusion mechanisms behind low temperature oxygen mobility.…”

“…An important example is stoichiometric and semiconducting La 2 CuO 4.0 , which can be transformed into a superconductor with a T c of 42 K when intercalated with oxygen, up to a stoichiometry corresponding to La 2 CuO 4.07 [1]. Other phases exist where the extra oxygen stoichiometry can attain important values as is the case for (Pr/Nd) 2 NiO 4+ , or La 2 CoO 4+ , with 0 ≤ ≤ 0.25, while the transition metal changes its valence state from pure 2+ to a mixed valence state of equally 2+/3+. The uptake of oxygen ions plays also a crucial role for low temperature oxygen mobility as has been shown recently in a combination of inelastic neutron scattering studies together with DFT-based simulations for Nd 2 NiO 4+ [2].…”

“…Other phases exist where the extra oxygen stoichiometry can attain important values as is the case for (Pr/Nd) 2 NiO 4+ , or La 2 CoO 4+ , with 0 ≤ ≤ 0.25, while the transition metal changes its valence state from pure 2+ to a mixed valence state of equally 2+/3+. The uptake of oxygen ions plays also a crucial role for low temperature oxygen mobility as has been shown recently in a combination of inelastic neutron scattering studies together with DFT-based simulations for Nd 2 NiO 4+ [2]. The main outcome of these investigations was that oxygen mobility has been simulated to take place already at ambient temperature in a time interval of some ps.…”