Molecular dynamics study of oxygen diffusion in Pr2NiO4+δ

Abstract

Oxygen transport in tetragonal Pr 2 NiO 4+d has been investigated using molecular dynamics simulations in conjunction with a set of Born model potentials. Oxygen diffusion in Pr 2 NiO 4+d is highly anisotropic, occurring almost entirely via an interstitialcy mechanism in the a-b plane. The calculated oxygen diffusivity has a weak dependence upon the concentration of oxygen interstitials, in agreement with experimental observations. In the temperature range 800-1500 K, the activation energy for migration varied between 0.49 and 0.64 eV depending upon the degree of hyperstoichiometry. The present results are compared to previous work on oxygen self-diffusion in related K 2 NiF 4 structure materials.

Interstitialcy diffusion of oxygen in tetragonal La2CoO4+δ

“…We observe that the equatorial oxygen site also has a strongly anisotropic thermal ellipsoid. This is similar to the one observed experimentally by Skinner 9 and MD calculations 17 in La 2 NiO 4+d , MD calculations in Pr 2 NiO 4+d , 26 and the maximum entropy method results of Yashima et al 14 for related oxides. The oxygen density of the apical oxygen is consistent with the DFT findings of octahedral tilting during the migration of the interstitial, shown on the LHS of Fig.…”

“…Previous MD calculations in Pr 2 NiO 4+d predicted that increases in the oxygen hyperstoichiometry can lead to a ''stiffening'' of the lattice and an increase of the migration energy barriers for oxygen interstitials. 26 While both the oxygen hyperstoichiometry and the higher valence B-site cations consistently imply a reduction in the oxygen diffusivity, the effect of both factors has yet to be systematically studied on the diffusion of oxygen in A 2 BO 4 materials. In the present study, using computational methods at two different scales, we assess a new model system, the tetragonal La 2 CoO 4+d , where the Ni of La 2 NiO 4+d is replaced with the higher valency Co.…”

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…[ 262,263 ] Most common Ln 2 NiO 4 (Ln = lanthanide) oxides belong to such a lattice structure, and become intriguing due to their oxygen ion conducting capabilities through intrinsic oxygen, without the necessity of forming oxygen hypo-stoichiometry through ionic doping. [264][265][266] The layer-structured Ln 2 NiO 4 can accommodate extra oxygen in its LnO rock-salt layer and bring about an anisotropic oxygen ion conducting property. [ 183,267,268 ] The tendency towards oxygen incorporation can be explained by a reduction of the mismatch between perovskite and rock salt layers due to i) a decrease of the average Ni-O bond distance caused by partial oxidation of Ni 2+ to Ni 3+ and ii) an increase of the average Ln-O distance due to a higher average coordination number of the lanthanide ions.…”

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

“…[5][6] Consequently, oxygen diffusion in the RP 214 phases can potentially occur via mechanisms associated with either oxygen interstitials or oxygen vacancies, or both. Recent neutron scattering studies 7 and molecular dynamic simulations [8][9][10] indicate that oxygen diffusion in the hyperstoichiometric RP 214 phases involves spontaneous migration of oxygen interstitials along with their neighboring apical oxygens from the rocksalt layers. Such an oxygen interstitialcy (push-pull) diffusion mechanism takes place anisotropically in the RP 214 structure, leading to significantly different oxygen ion transport along different orientations.…”