Polaronic structure of excess electrons and holes for a series of bulk iron oxides

Ahart, Christian S.; Blumberger, Jochen; Rosso, Kevin M.

doi:10.1039/c9cp06482f

Cited by 16 publications

(47 citation statements)

References 78 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In previous work we found that the excess electron in hematite is delocalized over two neighboring iron sites in the DFT electronic ground state. 26 According to electron transfer theory, this suggests that electronic coupling between 1-site localized excess electronic states is so large that they are are no longer stable states, that is, they no longer correspond to a minimum of the ground state potential energy surface. This is the case as soon as H ab > λ/2.…”

Section: Resultsmentioning

confidence: 99%

“…Though, one early estimate reported by Rosso and co-workers 17 for electron mobility is within a factor of 1.6 of our current best estimate. In previous work 26 we attributed the larger reorganization energy of cluster models to the absence of lattice strain effects present in the bulk structure, as well as the use of Hartree–Fock calculation which tends to overbind excess charge.…”

Section: Discussionmentioning

confidence: 99%

“… 45 , 46 In previous work we demonstrated that the standard definition of HSE06 with 25% HFX overestimates the experimental band gap of 2.2 eV as 3.6 eV, 47 and does not satisfy the generalized Koopmans condition. 26 …”

Section: Methodsmentioning

confidence: 99%

“…Initial coordinates were taken from the experimental crystal structure for hematite, 48 with geometry optimization converged until the residual forces were smaller than 0.02 eV/Å. For a more complete discussion of the structure and setup of bulk hematite refer to ref ( 26 ). The only change in this work was that the planewave cutoff was tightened from 400 to 600 Ry to aid in the verification of degenerate structures.…”

Section: Methodsmentioning

confidence: 99%

“…We have demonstrated that the electron hole polaron localizes on a single iron atom, with octahedral distortion of the surrounding iron–oxygen bonds and a change in spin moment of +0.66, consistent with hybrid DFT 23 and Hartree–Fock 18 calculations from other groups. The electron polaron however delocalizes equally across two neighboring iron atoms as a consequence of the lower reorganization energy for electrons compared to holes, 26 with a smaller change in spin moment of +0.23 over each iron atom.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

2022

Self Cite

View full text Add to dashboard Cite

Transition metal oxide materials have attracted much attention for photoelectrochemical water splitting, but problems remain, e.g. the sluggish transport of excess charge carriers in these materials, which is not well understood. Here we use periodic, spin-constrained and gap-optimized hybrid density functional theory to uncover the nature and transport mechanism of holes and excess electrons in a widely used water splitting material, bulk-hematite (α-Fe 2 O 3 ). We find that upon ionization the hole relaxes from a delocalized band state to a polaron localized on a single iron atom with localization induced by tetragonal distortion of the six surrounding iron–oxygen bonds. This distortion is responsible for sluggish hopping transport in the Fe-bilayer, characterized by an activation energy of 70 meV and a hole mobility of 0.031 cm 2 /(V s). By contrast, the excess electron induces a smaller distortion of the iron–oxygen bonds resulting in delocalization over two neighboring Fe units. We find that 2-site delocalization is advantageous for charge transport due to the larger spatial displacements per transfer step. As a result, the electron mobility is predicted to be a factor of 3 higher than the hole mobility, 0.098 cm 2 /(V s), in qualitative agreement with experimental observations. This work provides new fundamental insight into charge carrier transport in hematite with implications for its photocatalytic activity.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

2022

Self Cite

View full text Add to dashboard Cite

show abstract

Photothermal‐boosted polaron transport in Fe₂O₃ photoanodes for efficient photoelectrochemical water splitting

Huang

Cao

et al. 2023

Carbon Energy

View full text Add to dashboard Cite

Introduction of the photothermal effect into transition‐metal oxide photoanodes has been proven to be an effective method to improve the photoelectrochemical (PEC) water‐splitting performance. However, the precise role of the photothermal effect on the PEC performance of photoanodes is still not well understood. Herein, spinel‐structured ZnFe2O4 nanoparticles are deposited on the surface of hematite (Fe2O3), and the ZnFe2O4/Fe2O3 photoanode achieves a high photocurrent density of 3.17 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (VRHE) due to the photothermal effect of ZnFe2O4. Considering that the hopping of electron small polarons induced by oxygen vacancies is thermally activated, we clarify that the main reason for the enhanced PEC performance via the photothermal effect is the promoted mobility of electron small polarons that are bound to positively charged oxygen vacancies. Under the synergistic effect of oxygen vacancies and the photothermal effect, the electron conductivity and PEC performance are significantly improved, which provide fundamental insights into the impact of the photothermal effect on the PEC performance of small polaron‐type semiconductor photoanodes.

show abstract

Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

et al. 2023

Self Cite

View full text Add to dashboard Cite

Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic-and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems. A second key advance is new experimental evidence for what scientists hypothesized but could not test previously, namely, interfacial chemical reactions are frequently driven by "anomalies" or "non-idealities" such as defects, nanoconfinement, and other nontypical chemical structures. Third, progress in computational chemistry has yielded new insights that allow a move beyond simple schematics, leading to a molecular model of these complex interfaces. In combination with surfacesensitive measurements, we have gained knowledge of the interfacial structure and dynamics, including the underlying solid surface and the immediately adjacent water and aqueous ions, enabling a better definition of what constitutes the oxide− and silicate−water interfaces. This critical review discusses how science progresses from understanding ideal solid−water interfaces to more realistic systems, focusing on accomplishments in the last 20 years and identifying challenges and future opportunities for the community to address. We anticipate that the next 20 years will focus on understanding and predicting dynamic transient and reactive structures over greater spatial and temporal ranges as well as systems of greater structural and chemical complexity. Closer collaborations of theoretical and experimental experts across disciplines will continue to be critical to achieving this great aspiration.

show abstract

Polaronic structure of excess electrons and holes for a series of bulk iron oxides

Abstract: With the use of a gap-optimized hybrid functional and large supercells, it is found that while the electron hole polaron generally localises onto a single iron site, the electron polaron localises across two iron sites of the same spin layer.

Cited by 16 publications

References 78 publications

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

Photothermal‐boosted polaron transport in Fe₂O₃ photoanodes for efficient photoelectrochemical water splitting

Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

Contact Info

Product

Resources

About

Polaronic structure of excess electrons and holes for a series of bulk iron oxides

Abstract: With the use of a gap-optimized hybrid functional and large supercells, it is found that while the electron hole polaron generally localises onto a single iron site, the electron polaron localises across two iron sites of the same spin layer.

Cited by 16 publications

References 78 publications

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

Electron and Hole Mobilities in Bulk Hematite from Spin-Constrained Density Functional Theory

Photothermal‐boosted polaron transport in Fe2O3 photoanodes for efficient photoelectrochemical water splitting

Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

Contact Info

Product

Resources

About

Photothermal‐boosted polaron transport in Fe₂O₃ photoanodes for efficient photoelectrochemical water splitting