Tuning the electronic structure of SrTiO3/SrFeO3−<i>x</i> superlattices via composition and vacancy control

Berger, Robert; Broberg, Daniel; Neaton, Jeffrey B.

doi:10.1063/1.4869955

Cited by 8 publications

(6 citation statements)

References 35 publications

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“…In general, the energies of the configurations without Fe–V O [Figure (iii)] are 0.6 eV higher than those of the system with Fe–V O –Fe, and the configurations become even less stable when two neighboring Fe atoms are present without V O nearby [Figure (iv)]. These observations suggest a tendency for short-range ordering of V O around Fe ions, consistent with other computational studies. ,,, The presence of V O in the first coordination shell of Fe ion has also been revealed through Fe K-edge X-ray absorption spectroscopy . Therefore, our results are consistent with experiments showing that Fe atoms are largely 5-fold coordinated, whereas Ti atoms remain 6-fold coordinated…”

Section: Resultssupporting

confidence: 81%

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

2018

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As mixed ionic–electronic conductors (MIECs), ABO3 perovskite oxides and derivative compounds are candidates for applications such as solid oxide fuel and electrolysis cells. Understanding the atomic configuration and electronic structure of MIECs is important because they form the basis of ionic and electronic conductivities; but it is challenging because the materials tend to be non-dilute systems with substantial partial occupancies of the perovskite sublattices. In this work, we present a computational model for Fe-substituted SrTiO3 (STF, SrTi1–x Fe x O3–x/2+δ), a representative perovskite-derivative MIEC, by considering it as a mixture of perovskite SrTiO3 (x = 0, δ = 0) and brownmillerite Sr2Fe2O5 (x = 1, δ = 0). Our model accounts for disorder in the form of Ti and Fe species on the perovskite B-site sublattice and of O atoms and vacancies VO on the oxygen sublattice. The defect chemistry and electronic structure of STF across the full composition range 0 ≤ x ≤ 1 and for small |δ| is addressed within the framework of first-principles density functional theory. We find that this model of the STF solid solution reproduces experimentally known features such as short-range ordering between Fe and VO and thermodynamic influence on the oxygen content in STF. We illustrate how the electronic structure of STF systematically evolves from the characteristics of end-member compounds, SrTiO3 and Sr2Fe2O5, and establish the effects of nonzero δ on the type of electronic carriers present. These findings confirm that the SrTi1–x Fe x O3–x/2+δ framework is a useful description for this material system, providing a systematic understanding of structure–property relations in the nondilute perovskite mixture. Although this work focuses on STF, the underlying approach may be applicable to other mixtures of perovskite oxides and ordered oxygen vacancy compounds.

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Section: Resultssupporting

confidence: 81%

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

2018

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“…The Hubbard-U term was added to the DFT (GGA) energy functional to characterize the 3d and 4f orbital structure of iron (Fe) and titanium (Ti). The values of U eff = U – J were set to 6.31 and 5.0 eV for Ti and Fe, respectively. , The oxygen vacancy formation energy of an oxygen vacancy was calculated from the energy difference between the total energy contained by the V O - and the sum of the total energy of the pristine and the chemical potential of an oxygen atom in an O 2 molecule. The difference between the total energy stored by the V O - and the sum of the chemical potential of the oxygen atom in an O 2 molecule and the total energy of the pristine was used to determine oxygen vacancy formation energy.…”

Section: Experimental Part Including Materials Synthesis and Methodsmentioning

confidence: 99%

Modulating the Energy Band Structure of the Mg-Doped Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3−δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells

Rauf

Hanif

Mushtaq

et al. 2022

ACS Appl. Mater. Interfaces

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Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr0.5Pr0.5Fe0.4Ti0.6O3−δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr0.5Pr0.5Fe0.4–x Mg x Ti0.6O3−δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3−δ (SPFMg0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm–1 along with an attractive fuel cell performance of 0.83 W cm–2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO3−δ and Sr0.5Pr0.5Fe0.4–x Mg x Ti0.6O3−δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr0.5Pr0.5Fe0.4Ti0.6O3−δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.

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“…The strong on-site coulomb interaction on the d-orbital electrons on the Fe sites was treated with the generalized gradient approximation (GGA) + U approach. We adopted U eff = 4 eV for Hund's exchange interaction, which have been proven to give reasonable predictions of both geometric and electronic structures in previous works (42). Charge distribution was examined with the DDEC06 method, which is a refinement of the Density Derived Electrostatic and Chemical (DDEC) approach (38).…”

Section: Computational Toolsmentioning

confidence: 99%

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

et al. 2020

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Acceptor-doped, redox-active perovskite oxides such as La0.8Sr0.2FeO3 (LSF) are active for ethane oxidation to COx but show poor selectivity to ethylene. This article reports molten Li2CO3 as an effective “promoter” to modify LSF for chemical looping–oxidative dehydrogenation (CL-ODH) of ethane. Under the working state, the redox catalyst is composed of a molten Li2CO3 layer covering the solid LSF substrate. The molten layer facilitates the transport of active peroxide (O22−) species formed on LSF while blocking the nonselective sites. Spectroscopy measurements and density functional theory calculations indicate that Fe4+→Fe3+ transition is responsible for the peroxide formation, which results in both exothermic ODH and air reoxidation steps. With >90% ethylene selectivity, up to 59% ethylene yield, and favorable heat of reactions, the core-shell redox catalyst has an excellent potential to be effective for intensified ethane conversion. The mechanistic findings also provide a generalized approach for designing CL-ODH redox catalysts.

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Tuning the electronic structure of SrTiO3/SrFeO3−x superlattices via composition and vacancy control

Cited by 8 publications

References 35 publications

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

Modulating the Energy Band Structure of the Mg-Doped Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3−δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

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Tuning the electronic structure of SrTiO3/SrFeO3−x superlattices via composition and vacancy control

Cited by 8 publications

References 35 publications

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi1–xFexO3–x/2+δ Considered as a Mixture of SrTiO3 and Sr2Fe2O5

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi1–xFexO3–x/2+δ Considered as a Mixture of SrTiO3 and Sr2Fe2O5

Modulating the Energy Band Structure of the Mg-Doped Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3−δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

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Resources

About

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

Atomic Modeling and Electronic Structure of Mixed Ionic–Electronic Conductor SrTi_1–xFe_xO_3–x/2+δ Considered as a Mixture of SrTiO₃ and Sr₂Fe₂O₅

Modulating the Energy Band Structure of the Mg-Doped Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3−δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells