Self-doping and the role of oxygen vacancies in the magnetic properties of cubic BaFeO3−δ

Ribeiro, Bernardete; Godinho, M.; Cardoso, Cláudia; Borges, R. P.; Gasche, T.

doi:10.1063/1.4792664

Cited by 24 publications

(40 citation statements)

References 18 publications

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“…The FM spin state was identified as the ground state, this is consistent with previous DFT+U studies of parallel magnetic orderings of cubic BFO and SOFC operating conditions. 43,57 However, experimental analysis of the cubic stoichiometric BFO, identified an A-AFM type spin-spiral state below 111K, and FM above. 22 In relation to this, other DFT work studied a more precise helical spin ordering and found an However, the same study also identified a small energy barrier (0.017 meV per unit cell) for the transition from AFM to FM structures.…”

Section: Oxygen Deficiencymentioning

confidence: 99%

“…Next, the electronic structure of BFO was explored in the projected density of states (PDOS), Figure 3, which revealed a nearly half-metallic electronic structure with a high Fe spin state; this is consistent with previous DFT+U studies. 57 …”

Section: Oxygen Deficiencymentioning

confidence: 99%

“…,58 The deep energy of the Fe 3d majority bands and the dominance of the O 2p bands at the Fermi level suggest a metal to ligand charge transfer 57. Based on this, the O 2p states at the Fermilevel and above are considered hole-type.…”

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confidence: 99%

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A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

Baiyee

Chen

Ciucci

2015

Phys. Chem. Chem. Phys.

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BaFeO3-δ (BFO)-based perovskites have emerged as cheap and effective oxygen electrocatalysts for oxygen reduction reaction at high temperatures. The BFO cubic phase facilitates a high oxygen deficiency and is commonly stabilised by partial substitution. Understanding the electronic mechanisms of substitution and oxygen deficiency is key to rational material design, and can be realised through DFT analysis. In this work an in-depth first principle DFT+U study is undertaken to determine site distinctive characteristics for 12.5%, Y, La and Ce substitutions in BFO. In particular, it is shown that B-site doped structures exhibit a lower energy cost for oxygen vacancy formation relative to A site doping and pristine BFO. This is attributed to the stabilisation of holes in the oxygen sub-lattice and increased covalency of the Fe-O bonds of the FeO6 octahedra in B-site-substituted BFO. Charge analysis shows that A-site substitution amounts to donor doping and consequently impedes the accommodation of other donors (i.e. oxygen vacancies). However, A-site substitution may also exhibit a higher electronic conductivity due to less lattice distortion for oxygen deficiency compared to B-site doped structures. Furthermore, analysis of the local structural effects provides physical insight into stoichiometric expansions observed for this material.

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Section: Oxygen Deficiencymentioning

confidence: 99%

Section: Oxygen Deficiencymentioning

confidence: 99%

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A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

Baiyee

Chen

Ciucci

2015

Phys. Chem. Chem. Phys.

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“…Unfortunately, it is difficult to synthesize stoichiometric cubic BFO because the high valence Fe 4+ is not favorable in this system since the Fe 3d band energy is lower than O 2p band, introducing a negative ligand to metal charge transfer 50 energy. 13 Although phase transition of the mixed phase to pure cubic structure is observed at around 900 °C, 14 application of this material at intermediate temperature is not feasible because the material performance substantially decreases due to the presence of the vacancy-ordered monoclinic phase. Nevertheless, several 55 synthesis methods have been used to obtain phase-pure cubic BFO at relatively low temperatures.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the effect of La A-site substitution on oxygen ion diffusion and oxygen catalysis in perovskite BaFeO₃by data-mining molecular dynamics and density functional theory

Chen

Baiyee

Ciucci

2015

Phys. Chem. Chem. Phys.

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BaFeO3 (BFO) is a promising parent material for high-temperature oxygen catalysis. The effects of La substitution on the oxygen ion diffusion and oxygen catalysis in A-site La-substituted BFO are studied by combining data-driven molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The data-driven MD simulations are capable of providing atomic level information regarding oxygen jumps at different sites, bridging the resolution gap of analysis between MD and DFT. The simulations identify several effects due to the introduction of La. First, according to simple electroneutrality considerations and DFT calculations, La tends to decrease the concentration of oxygen vacancies in BFO. Second, La substitution lowers the activation energy of local oxygen migration, providing faster paths for oxygen diffusion. The MD analysis predicts a higher hopping rate through La-containing bottlenecks as well as easier oxygen jumps from the La-rich cages and lower dwell times of oxygen in those cages. DFT calculations confirm a lower migration energy through La-containing bottlenecks. Third, the electrocatalytic activity of the material decreases with La, as indicated by a lower O p-band center and higher oxygen vacancy formation energies.

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“…For the FM order and experimental lattice parameter of the cubic BFO, the calculated magnetic moment varies between 3.0 µ B and 3.4 µ B per f.u., 15,16 depending on the model approximation used to treat the exchange-correlation effects. According to the ab initio investigation by Ribeiro et al 17 the FM solution in the stoichiometric BFO is energetically favorable against the possible AFM configurations while the FM moment is about 3.6 µ B . A helical magnetic ordering in BFO, which is usually discussed in the context of SrFeO 3 and CaFeO 3 , 18 has been investigated from first principles by Zhi Li et al 19,20 The authors anticipate that the G-type helical solution can be fixed, keeping the reduced volume and, simultaneously, using the Hubbard parametrization which treats electronic correlations beyond the standard of the local density approximation.…”

Section: Introductionmentioning

confidence: 99%

Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties ofBaFeO3−δ

et al. 2016

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We studied structural, electronic and magnetic properties of a cubic perovskite BaFeO 3−δ (0 ≤ δ ≤ 0.5) within the density functional theory using a generalized gradient approximation and a GGA+U method. According to our calculations, BaFeO3 in its stoichiometric cubic structure should be half-metallic and strongly ferromagnetic, with extremely high Curie temperature (TC ) of 700 -900 K. However, a such estimate of TC disagrees with all available experiments, which report that TC of the BaFeO3 and undoped BaFeO 3−δ films varies between 111 K and 235 K or, alternatively, that no ferromagnetic order was detected there. Fitting the calculated x-ray magnetic circular dichroism spectra to the experimental features seen for BaFeO3, we concluded that the presence of oxygen vacancies in our model enables a good agreement. Thus, the relatively low TC measured in BaFeO3 can be explained by oxygen vacancies intrinsically presented in the material. Since iron species near the O vacancy change their oxidation state from 4+ to 3+, the interaction between Fe 4+ and Fe 3+ , which is antiferromagnetic, weakens the effective magnetic interaction in the system, which is predominantly ferromagnetic. With increasing δ in BaFeO 3−δ , its TC decreases down to the critical value when the magnetic order becomes antiferromagnetic. Our calculations of the electronic structure of BaFeO 3−δ illustrate how the ferromagnetism originates and also how one can keep this cubic perovskite robustly ferromagnetic far above the room temperature.

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Self-doping and the role of oxygen vacancies in the magnetic properties of cubic BaFeO3−δ

Cited by 24 publications

References 18 publications

A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

Unraveling the effect of La A-site substitution on oxygen ion diffusion and oxygen catalysis in perovskite BaFeO₃by data-mining molecular dynamics and density functional theory

Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties ofBaFeO3−δ

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Self-doping and the role of oxygen vacancies in the magnetic properties of cubic BaFeO3−δ

Cited by 24 publications

References 18 publications

A DFT+U study of A-site and B-site substitution in BaFeO3−δ

A DFT+U study of A-site and B-site substitution in BaFeO3−δ

Unraveling the effect of La A-site substitution on oxygen ion diffusion and oxygen catalysis in perovskite BaFeO3by data-mining molecular dynamics and density functional theory

Impact of oxygen doping and oxidation state of iron on the electronic and magnetic properties ofBaFeO3−δ

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A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

A DFT+U study of A-site and B-site substitution in BaFeO_3−δ

Unraveling the effect of La A-site substitution on oxygen ion diffusion and oxygen catalysis in perovskite BaFeO₃by data-mining molecular dynamics and density functional theory