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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on FeO by Materials Project

FeO is Moissanite-4H structured and crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are two inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to four O2- atoms to form corner-sharing FeO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.10 Å. In the second Fe2+ site, Fe2+ is bonded to four O2- atoms to form corner-sharing FeO4 tetrahedra. There are a spread of Fe–O bond distances ranging from 1.98–2.13 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four Fe2+ atoms to form corner-sharing OFe4 tetrahedra. In the second O2- site, O2- is bonded to four Fe2+ atoms to form corner-sharing OFe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeO by Materials Project

FeO is Halite, Rock Salt-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to six equivalent O2- atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 4–5°. There are two shorter (2.09 Å) and four longer (2.27 Å) Fe–O bond lengths. In the second Fe2+ site, Fe2+ is bonded to six equivalent O2- atoms to form a mixture of corner and edge-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 4–5°. There are four shorter (2.17 Å) and two longer (2.25 Å) Fe–O bond lengths. O2- is bonded to six Fe2+ atoms to form a mixture of corner and edge-sharing OFe6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeO by Materials Project

FeO is Molybdenum Carbide MAX Phase-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are twelve inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.15–2.25 Å. In the second Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.15–2.27 Å. In the third Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.15–2.25 Å. In the fourth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.14–2.27 Å. In the fifth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.14–2.26 Å. In the sixth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.16–2.25 Å. In the seventh Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.14–2.26 Å. In the eighth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 45–49°. There are a spread of Fe–O bond distances ranging from 2.15–2.28 Å. In the ninth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.14–2.26 Å. In the tenth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.15–2.31 Å. In the eleventh Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 46–49°. There are a spread of Fe–O bond distances ranging from 2.12–2.27 Å. In the twelfth Fe2+ site, Fe2+ is bonded to six O2- atoms to form a mixture of edge, corner, and face-sharing FeO6 octahedra. The corner-sharing octahedra tilt angles range from 45–49°. There are a spread of Fe–O bond distances ranging from 2.16–2.26 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the second O2- site, O2- is bonded in a 6-coordinate geometry to six Fe2+ atoms. In the third O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the fourth O2- site, O2- is bonded in a 6-coordinate geometry to six Fe2+ atoms. In the fifth O2- site, O2- is bonded in a 6-coordinate geometry to six Fe2+ atoms. In the sixth O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the seventh O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the eighth O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the ninth O2- site, O2- is bonded in a 6-coordinate geometry to six Fe2+ atoms. In the tenth O2- site, O2- is bonded in a 6-coordinate geometry to six Fe2+ atoms. In the eleventh O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids. In the twelfth O2- site, O2- is bonded to six Fe2+ atoms to form a mixture of distorted edge and corner-sharing OFe6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Atomically Revealing Bulk Point Defect Dynamics in Hydrogen‐Driven γ‐Fe 2 O 3 → Fe 3 O 4 → FeO Transformation

Understanding how point defects in the bulk govern redox transformations is essential for advancing hydrogen-based metal production and designing high-performance oxide materials. This study reveals the atomic-scale mechanisms driving hydrogen-induced reduction of γ-Fe 2 O 3 to Fe 3 O 4 , focusing on how bulk vacancy dynamics dictate structural evolution and reaction kinetics. A key finding is the pronounced contrast in defect behavior between the two oxides: in γ-Fe 2 O 3 , intrinsic Fe vacancies promote oxygen vacancy clustering, destabilizing the local lattice and driving nanopore formation. In contrast, Fe 3 O 4 exhibits a higher oxygen vacancy formation energy and lacks intrinsic Fe vacancies, suppressing vacancy aggregation and maintaining a dense, pore-free structure. This divergence governs distinct reduction pathways—γ-Fe 2 O 3 undergoes an interface-reaction-limited transformation confined to the γ-Fe 2 O 3 /Fe 3 O 4 boundary, while Fe 3 O 4 supports a uniform increase in oxygen vacancy concentration, enabling bulk-phase reduction to lower-oxide FeO. Integrated in situ electron microscopy and density functional theory modeling uncover a vacancy-mediated mechanism, where synergistic cation-anion vacancy dynamics steer microstructure evolution and phase progression. These insights highlight the critical role of vacancy dynamics in controlling oxide reactivity and offer a pathway toward vacancy engineering to enhance reduction kinetics in hydrogen metallurgy and to tailor porosity, reactivity, and structural resilience in oxide-based catalysts and energy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Nickel B-site substitution in bulk Sr 1-x Ca x FeO 3 perovskite oxygen carriers: Benefits and limitations

We report oxygen (O 2 ) storage materials often rely on the presence of cobalt (Co) to reduce the thermodynamic penalty and increase the kinetics necessary for efficient O 2 storage and release. In this work, we investigate nickel (Ni) as an alternative B-site dopant in Sr 1-x Ca x FeO 3 to identify Co-free carriers that still show improved kinetics at low temperatures. In fact, we show a substantial increase in the reversible O2 release rate through mild Ni B-site substitution (y = 0.06) in select Sr 1-x Ca x Fe 1-y Ni y O 3 systems at 400 to 500 °C, reaching 2.00 wt.% O 2 release up to approximately 75% faster than Ni-free systems. To explain the role of Ni in these systems, we use density functional theory to calculate the O 2 vacancy (V O ) formation energy from separate metal-oxygen (M-O) bonding and relaxation components. We computationally show elongated Ni-O bonds are directly responsible for the decrease in V O upon Ni substitution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Air separation and N 2 purification with Ba 0.15 Sr 0.85 FeO 3-$δ$ via a two-step thermochemical process

Thermochemical air separation to produce high-purity N 2 was demonstrated in a vertical tube reactor via a two-step reduction–oxidation cycle with an A-site substituted perovskite Ba 0.15 Sr 0.85 FeO 3–δ (BSF1585). BSF1585 particles were synthesized and characterized in terms of their chemical, morphological, and thermophysical properties. A thermodynamic cycle model and sensitivity analysis using computational heat and mass transfer models of the reactor were used to select the system operating parameters for a concentrating solar thermal-driven process. Thermal reduction up to 800 °C in air and temperature-swing air separation from 800 °C to minimum temperatures between 400 and 600 °C were performed in the reactor containing a 35 g packed bed of BSF1585. The reactor was characterized for dispersion, and air separation was characterized via mass spectrometry. Gas measurements indicated that the reactor produced N 2 with O 2 impurity concentrations as low as 0.02 % for > 30 min of operation. Additionally, a parametric study of air flow rates suggested that differences in observed and thermodynamically predicted O 2 impurities were due to imperfect gas transport in the bed. Temperature swing reduction/oxidation cycling experiments between 800 and 400 °C in air were conducted with no statistically significant degradation in N 2 purity over 50 cycles.

14 SOLAR ENERGY↗
DOE OSTI2021

Air separation via a two-step solar thermochemical cycle based on (Ba,La) x Sr 1-x FeO 3-δ : Thermodynamic analysis

A two-step solar thermochemical cycle was considered for air separation to produce N2 based on (Ba,La) x Sr 1-x FeO 3-δ perovskite reduction/oxidation (redox) reactions for A-site fractions of 0 ≤ x ≤ 0.2. The cycle steps encompassed (1) thermal reduction and O 2 release via concentrated solar input and (2) re-oxidation with air to uptake O 2 and produce high-purity N 2 . Thermogravimetry at temperatures between 400 and 1100 °C in atmospheres of 0.005 to 90% O 2 /Ar at 1 bar was performed to measure equilibrium nonstoichiometries. The compound energy formalism was applied to model redox thermodynamics for both Ba 2+ and La 3+ substitution. Non-linear regression was used to determine the empirical parameters based on the thermogravimetric measurements. The model was used to define partial molar reaction enthalpies and entropies and predicted equilibrium oxygen nonstoichiometry as functions of oxide stoichiometry, site fraction, temperature, and O 2 partial pressure. The thermodynamic analysis showed the materials are appealing for air separation at temperatures below 800 °C.

42 ENGINEERING↗
DOE OSTI2022

Overcoming significant challenges in extracting off-stoichiometric thermodynamics using the compound energy formalism through complementary use of experimental and first principles data: A case study of Ba 1-x Sr x FeO 3-δ

The compound energy formalism (CEF) is a powerful framework to describe the thermodynamics of metal oxides as a function of off-stoichiometry, temperature, and composition. The thermodynamic properties are crucial materials design attributes in metal oxide-based oxygen-exchange chemical processes. Despite the richness of information an accurate CEF model provides, a method to determine a unique and accurate fit for oxygen exchange materials remains elusive. This contribution details a method for fitting the CEF model that overcomes the current fitting challenges through three innovations: 1) the combination of density functional theory calculations with experimental data decorrelates excess terms and delineates the enthalpic/entropic contributions to the Gibbs free energy; 2) a systematic determination of the important CEF model terms, removing thermodynamic predetermining human intervention; 3) a self-consistent solution of the starting oxygen offstoichiometry (δ 0 ) of thermogravimetric measurements. Thus, our method enables the reliable extraction of off-stoichiometric metal oxide thermodynamic properties and facilitates rapid materials compositional screening, and reliable process design of systems dependent on off-stoichiometric redox-active metal oxides. We apply this method to a Ba x Sr 1-x FeO 3-δ test case. We find by systematically examining the performance of the CEF model fit with and without each innovation that all three innovations are necessary for an accurate fit. We determined that reduction enthalpy is higher and more sensitive to off-stoichiometry when the Sr fraction is large (139.5 and 185.3 kJ/mol O 2 for SrFeO 3 at δ = 0 and δ = 0.5, respectively vs. nearly constant 83 kJ/mol O 2 for BaFeO 3 ). However, the reduction entropy is mostly insensitive to Sr fraction, but highly dependent on δ suggesting larger contributions in the non-configurational entropy parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Isoconversional Kinetic Analysis of Oxygen Desorption for Sr 0.75 Ca 0.25 FeO 3-δ Perovskite in Dry and Steam-Based Environments

The desorption kinetics of Sr 0.75 Ca 0.25 FeO 3-δ perovskite material are examined in both dry and steam-based environments using redox gaseous products of a laboratory-scale fixed bed. First, desorption kinetics associated with the dry environment are proposed based on Friedman’s isoconversional method. It is found from the reconstructed reaction model that the desorption kinetics of this perovskite are controlled by a three-step mechanism, where hypothetically, the phase-boundary reaction rapidly prevails first, followed by diffusion and/or nucleation, and finally, unimolecular decay or random nucleation-controlled reaction. Subsequent analyses of the Arrhenius parameters indicated that both the early and later desorption stages, respectively, controlled by the phase boundary and unimolecular/random nucleation reactions, are associated with low energetic demand. In contrast, a high energetic penalty is required for the diffusion/nucleation reaction. Further, a satisfactory a priori verification of the proposed kinetics suggested that the three-step reaction mechanism reasonably describes the desorption of this perovskite in a dry environment. With the presence of steam in the desorption environment, oxygen production is substantially inhibited, but the hypothetical three-step mechanism is still found to control the desorption. Meanwhile, the primary effects of the steam on these mechanisms include the widening of the conversion extent associated with the diffusion/nucleation reaction, along with a higher energetic demand compared to the dry environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

JOINT APPOINTEE: Evolution of ferroelectric properties in SmxBi1-xFeO3 via automated Piezoresponse Force Microscopy across combinatorial spread libraries

Combinatorial spread libraries offer a innovative approach to explore the evolution of material properties over broad concentration, temperature, and growth parameter spaces. However, traditional limitation of this approach is the requirement for the read-out of functional properties across the library. Here we develop automated Piezoresponse Force Microscopy (PFM) for the exploration of combinatorial spread libraries and demonstrate its application in the SmxBi1-xFeO3 system with the ferroelectric-antiferroelectric morphotropic phase boundary. This approach relies on the synergy of the quantitative nature of PFM and the implementation of automated experiments that allow PFM-based sampling over macroscopic samples. The concentration dependence of pertinent ferroelectric parameters has been determined and used to develop the mathematical framework based on Ginzburg-Landau theory describing the evolution of these properties across the concentration space. We pose that a combination of automated scanning probe microscope and combinatorial spread library approach will emerge as an efficient research paradigm to close the characterization gap in the high-throughput materials discovery. We make the data sets open to the community and hope that this will stimulate other efforts to interpret and understand the physics of these systems.

Automated Microscopy, Combinatorial Library, Ferro↗
DOE OSTI2026

Continuity of reaction kinetics across the pressure and materials gaps in CO oxidation on FeO–Pt interfaces

Translating atomic-scale insights from surface science studies of model catalysts to practical powder catalysts remains a persistent challenge in heterogeneous catalysis. Here, in this study, we demonstrate mechanistic continuity across the pressure and materials gaps during CO oxidation at the FeO-Pt interface using in situ microscopy, spectroscopy and computational modelling. Under reaction conditions, coordinatively unsaturated Fe (Fe cus ) sites at the interface enable selective O 2 activation on CO-saturated surfaces, circumventing the CO-poisoning limitation of platinum-group metals. We identify parallel reaction pathways involving the *O 2 -*CO intermediate. Remarkably, activation energies remain consistent at 12-15 kJ mol −1 (0.12-0.16 eV) from ultrahigh vacuum to atmospheric pressures and from FeO/Pt(111) model catalysts to FeO/Pt powder catalysts, validating mechanistic insights derived from surface science studies. Our findings show an example of bridging the long-standing divide between model and practical catalyst systems, establishing an effective approach to capture catalytic behaviours under operational conditions and advancing mechanism-driven catalyst design.

03 NATURAL GAS↗
DOE OSTI2021

Combined multiplet theory and experiment for the Fe 2p and 3p XPS of FeO and Fe 2 O 3

The Al K alpha, 1486.6eV, based XPS of Fe 2p and Fe 3p for Fe(III) in Fe 2 O 3 and Fe(II) in FeO are compared with theoretical predictions based on ab initio wavefunctions that accurately treat the final, core-hole, multiplets. The principal objectives of this comparison are to understand the multiplet structure and to evaluate the use of both the 2p and 3p spectra in determining oxidation state. In order to properly interpret the features of these spectra and to use the XPS to provide atomistic insights as well as atomic composition, it is necessary to understand the origin of the multiplet energies and intensities. The theoretical treatment takes into account the ligand field and spin-orbit splittings, the covalent mixing of ligand and Fe 3d orbitals, and the angular momentum coupling of the open shell electrons. These effects lead to the distribution of XPS intensity into a large number of final, ionic, states that are only partly resolved with energies spread over a wide range of binding energies, BEs. For this reason, it is necessary to record the Fe 2p and 3p XPS spectra over a wide energy range which includes all the multiplets in the theoretical treatment as well as additional shake satellites. We also evaluate the effects of differing assumptions concerning the extrinsic background subtraction, to be sure our experimental spectrum may be fairly compared to the theory. In this work, we conclude that the Fe 3p XPS provides an additional means for distinguishing Fe(III) and Fe(II) oxidation states beyond just using the Fe 2p spectrum. In particular, with the use of the Fe 3p XPS, the depth of the material probed is about 1.5 times greater than for the Fe 2p XPS. In addition, a new type of atomic many-body effect that involves excitations into orbitals that have Fe f,$\ell$=3, symmetry has been shown to be important for the Fe 3p XPS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Beneficial Effect of Li 5 FeO 4 Lithium Source for Li-Ion Batteries with a Layered NMC Cathode and Si Anode

The energy density of lithium-ion batteries can be increased by replacing the traditional graphite anode with a high capacity silicon anode. However, volume changes and interfacial instabilities cause a large irreversible capacity and a continual loss of lithium during cycling, which lead to rapid capacity loss. In this work, we add Li 5 FeO 4 (LFO) to a LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC) cathode as a pre-lithiation additive, which increases the lithium inventory and extends the cycle life of Si-graphite/NMC full cells, and decreases the NMC particle degradation. LFO delivers a large 764 mAh g –1 LFO capacity below 4.7 V vs Li/Li + . By tuning the LFO content in Si-graphite/LFO-NMC full cells, we show higher capacity, improved retention, lower impedance, and superior rate performance compared to full cells without LFO. Post-test characterizations demonstrate that LFO inclusion in the cathode matrix leads to less NMC secondary particle segregation/cracking and a thinner surface reduced layer on the NMC particles. The beneficial effects of LFO endure after the lithium reserve has been exhausted, highlighting a lasting synergy between the lithium source and electrode active materials. This study introduces a new approach to simultaneously increase lithium inventory and reduce cathode degradation, and makes critical advances toward enabling Si anodes for lithium-ion batteries.

25 ENERGY STORAGE↗
NASA NTRS1975

Electrical resistivity surface for FeO-Fe2O3-P2O5 glasses

The dc electrical properties and microstructure of x(FeO-Fe2O3)-(100-x)P2O5 glasses were investigated up to a maximum of x = 75 mol %. Results indicate that, in general, the minimum resistivity of the glass does not occur at equal Fe(2+) and Fe(3+) concentrations, although for the special case where x = 55 mol % the minimum does occur at Fe(2+)/Fe total = 0.5, as reported by other investigators. Evidence presented shows that the position of the minimum resistivity is a function of total iron content. The minimum shifts to glasses richer in Fe(2+) at higher total iron concentrations.

Vaughan, J. G.↗
NASA NTRS1975

Liquid-solid equilibria involving spinel, ilmenite, and ferropseudobrookite in the system 'FeO'-Al2O3-TiO2 in contact with metallic iron

Phase relations in the liquidus temperature region of the system 'FeO'-Al2O3-TiO2 in contact with metallic iron, at a total pressure below 1 atm, have been determined by the quenching technique. Four invariant points have been located, with phase assemblages and temperatures as follows; wuestite, ulvoespinel, nercynite and liquid, 1306 C; ulvoespinel, ilmenite, ferropseudobrookite and liquid, 1340 C; ulvoespinel, hercynite, ferropseudobrookite and liquid, 1367 C; hercynite, ferropseudobrookite, corundum and liquid, 1465 C. The data obtained confirm the presence of a miscibility gap between titanate and aluminate spinels, and provide quantitative data for the effect of Al2O3 on mutual stability relations among spinel, ilmenite, and ferropseudobrookite phases in the presence of liquid at high temperatures and strongly reducing conditions. It is shown that Al2O3 has a strong stabilizing effect on the phase assemblage ferropseudobrookite and spinel relative to ilmenite.

Schreifels, W. A.↗