Mechanistic Analysis of Oxygen Vacancy Formation and Ionic Transport in Sr₃Fe₂O_7−δ

Abstract

The elucidation of the oxygen ionic transport mechanism in atomic scale is important for finding the essential element of the higher efficiency and the wider oxygen content range in the application such as three-way catalysis or SOFC. In this study, the oxygen ionic transport properties of Sr3Fe2O7−δ are investigated as a function of its oxygen content by using density functional theory within the GGA+U methods. The calculated activation energy in Sr3Fe2O6.0 exhibits a higher migration barrier of 1.35 eV, while those in Sr3Fe2O6.25–6.75 are below 1.09 eV. To elucidate the difference of activation energy in Sr3Fe2O7−δ, we calculated the electronic and magnetic properties, which vary depending on the oxygen content and should affect the oxygen ionic transport. In our calculation, the energy band gap of 2.2 eV and the G-type antiferromagnetic ordering in Sr3Fe2O6.0 are well reproduced. The insulating phase in Sr3Fe2O6.25–6.5 is reproduced, and the magnetic phase transition from antiferromagnetic to incommensurate antiferromagnetic ordering within the planar FeO2 is also reasonably reproduced within our collinear calculation. In terms of the oxygen diffusion, we found that the vacancy at the O3 site between the bilayers of FeO6 is energetically the most stable and the vacancy at the apical O3 site moves more easily to an adjacent equatorial O1 site of FeO6 than in other directions for vacancy redistribution. The obtained activation energy of the O1 → O3 pathway is 1.09 eV, which agrees with the experimental value. The added O3 atom induces Jahn–Teller distortion, which is related not only with the insulating phase in Sr3Fe2O6.25–6.5 but also with the lower activation energy in Sr3Fe2O6.25–6.75, compared with Sr3Fe2O6.0.

A first-principles study on divergent reactions of using a Sr3Fe2O7 cathode in both oxygen ion conducting and proton conducting solid oxide fuel cells

“…Structural optimization was carried out until the Hellmann-Feynman force on each atom was lower than 0.03 eVÅ À1 . All calculations were spin-polarized, 21,22 and the ferromagnetic (FM) states instead of antiferromagnetic (AFM) were used as indicated by Tadashi Ota et al 23 To predict the electronic structures more precisely, DFT + U method 24 was applied in all our calculations. Here, the value of U eff ¼ U À J ¼ 5.3 eV was applied for Fe ions, and the Coulomb (U) and exchange (J) parameters were not taken into account separately.…”

“…The conducting characteristics of Sr 3 Fe 2 O 7 is half-metallic, in good agreement with previous experimental and theoretical investigations on Sr 3 Fe 2 O 7 , facilitating the electron conduction. 12,23,29,30 To explore stable (001) surface for O 2 reduction investigation, ve types of (001) terminal surfaces can be clave, as illustrated in Fig. 2 and S1 † and noted as SrO-1, SrO-2, SrO-3, FeO-1 and FeO-2 terminal surfaces, respectively.…”

Oxidation and Storage Mechanisms for Nitrogen Oxides on Variously Terminated (001) Surfaces of SrFeO3−δ and Sr3Fe2O7−δ Perovskites

“…RP-type oxides Sr 3 Fe 2 O 7−δ have both superior NO x oxidation activity and NO x adsorption ability relative to the simple perovskite oxide SrFeO 3−δ . Recent X-ray absorption fine structure (XAFS) experiment 15 and the density functional theory (DFT) study 17 have revealed that the origin of superior catalytic activity of Sr 3 Fe 2 O 7−δ is attributed to the small activation energy for oxygen migration in bulk. Beyond these findings, the mechanism is still unknown for the NO x storage by the Sr-Fe perovskite.…”

Deep Bayesian local crystallography

“…Spiral magnetic order was observed by neutron diffraction 97 and provides a rare example of a magnetic cycloid arising from a ferromagnetic nearest neighbor competing with antiferromagnetic next-nearest exchange 98 . Further interest in this material arise from high oxygen mobility 99 . The preparation of a near stoichiometric compound requires high oxygen partial pressure 100 .…”

“…68 Further interest in this material arise from high oxygen mobility. 69 The preparation of a near stoichiometric compound requires high oxygen partial pressure. 70 The rVAE analysis of SFO is shown in Figure 7.…”