Thermodynamics of Fe oxides: Part II. Enthalpies of formation and relative stability of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>)

Majzlan, Juraj; Grevel, Klaus‐Dieter; Navrotsky, Alexandra

doi:10.2138/am-2003-5-614

Cited by 150 publications

(88 citation statements)

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“…Available experimental values [105] are also shown in figure for comparison. Among the 5 iron oxides and oxyhydroxides, magnetite is typically excluded from the experiments because all the other four compounds (goethite, lepidocrocite, maghemite, and hematite) can be rewritten as …”

Section: F Lepidocrocite (γ-Feooh)mentioning

confidence: 99%

“…The phase diagram shows that the free energy of goethite is lower than hematite at standard state, and this agrees with the calorimetry measurements. [105] In a wet environment, these phase diagrams predict that the formation of goethite will be more thermodynamically favorable than hematite; while dehydration (dry conditions) will cause goethite to transform into hematite given a suitable driving force.…”

Section: F Lepidocrocite (γ-Feooh)mentioning

confidence: 99%

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Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Guo

Barnard

2011

Phys. Rev. B

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Iron oxides and oxyhydroxides are challenging to model computationally as competing phases may differ in formation energies by only several kJ mol −1 , they undergo magnetization transitions with temperature, their structures may contain partially occupied sites or long-range ordering of vacancies, and some loose structures require proper description of weak interactions such as hydrogen bonding and dispersive forces. If structures and transformations are to be reliably predicted under different chemical conditions, each of these challenges must be overcome simultaneously, while preserving a high level of numerical accuracy and physical sophistication. Here we present comparative studies of structure, magnetization, and elasticity properties of iron oxides and oxyhydroxides using density functional theory calculations with plane-wave and locally-confined-atomic-orbital basis sets, which are implemented in VASP and SIESTA packages, respectively. We have selected hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and magnetite (Fe 3 O 4 ) as model systems from a total of 13 known iron oxides and oxyhydroxides; and use same convergence criteria and almost equivalent settings in order to make consistent comparisons. Our results show both basis sets can reproduce the energetic stability and magnetic ordering, and are in agreement with experimental observations. There are advantages to choosing one basis set over the other, depending on the intended focus. In our case, we find the method using PW basis set most appropriate, and combine our results to construct the first phase diagram of iron oxides and oxyhydroxides in the space of competing chemical potentials, generated entirely from first principles.keywords: iron oxides and oxyhydroxides; phase diagram; density functional theory; modeling and simulation.

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Section: F Lepidocrocite (γ-Feooh)mentioning

confidence: 99%

Section: F Lepidocrocite (γ-Feooh)mentioning

confidence: 99%

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Guo

Barnard

2011

Phys. Rev. B

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“…Thermodynamic properties and particle-size effects have been studied extensively for the goethite-hematite reaction (Langmuir 1971;Majzlan et al 2003a;Majzlan et al 2003b). Only recently was a detailed structural analysis of a natural crystal of goethite performed at ambient conditions, including anisotropic atomic-displacement parameters (Yang et al 2006).…”

Section: Introductionmentioning

confidence: 99%

“…To remain mostly in the stability field of goethite, we followed the dehydration boundary presented in Majzlan et al (2003b). Once a target pressuretemperature condition was achieved, the sample would stay at that condition for 30 minutes or less, depending on whether a CCD or image plate was used to record the pattern.…”

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confidence: 99%

Pressure-temperature stability studies of FeOOH using X-ray diffraction

Gleason

Jeanloz

Kunz

2008

American Mineralogist

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“…Another possibility is that cells use H 2 as a reductant for maghemite, similar to known iron reducers in the Geobacteraceae (Lovley, 2003). The ∆G f for maghemite is from Majzlan et al (2003), the ∆G f for magnetite is from Robie and Hemmingway (1995), and all other values are from Stumm and Morgan (1996).…”

Section: The Magnetite/maghemite Battery Hypothesismentioning

confidence: 99%

Geobiology of marine magnetotactic bacteria

Simmons¹

2006

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Magnetotactic bacteria (MTB) biomineralize intracellular membrane-bound crystals of magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ), and are abundant in the suboxic to anoxic zones of stratified marine environments worldwide. Their population densities (up to 10 5 cells ml −1 ) and high intracellular iron content suggest a potentially significant role in iron cycling, but very little is known about their population dynamics and regulation by environmental geochemistry.The MTB community in Salt Pond (Falmouth, MA), a small stratified marine basin, was used as a model system for quantitative community studies. Magnetiteproducing MTB predominate slightly above the oxic-anoxic interface and greigiteproducing MTB predominate in sulfidic waters. A quantitative PCR (QPCR) assay was developed and applied to enumerate four major groups of MTB in Salt Pond: magnetite-producing cocci, barbells, the greigite-producing many-celled magnetotactic prokaryote (MMP), and a greigite-producing rod. The barbells were identified as δ-Proteobacteria while the rod was identified as the first MTB in the γ-Proteobacteria. The MMP, previously thought to be a single species, consists of at least five clades with greater than 5% divergence in their 16s rRNA. Fluorescent in situ hybridization probes showed significant variation in clade abundances across a seasonal cycle in salt marsh productivity. FISH also showed that aggregates consist of genetically identical cells.QPCR data indicated that populations are finely layered around the oxic-anoxic interface: cocci immediately above the dissolved Fe(II) peak, barbells immediately below, the MMP in microsulfidic waters, and the greigite-producing rod in low numbers (100 cells ml −1 ) below the gradient region. The barbell reached 1-10% of total eubacteria in the late season, and abundances of cocci and barbells appeared to vary inversely. Calculations based on qPCR data suggest that MTB are significant unrecognized contributors to iron flux in stratified environments.Barbells can respond to high oxygen levels by swimming toward geomagnetic 2 south, the opposite of all previously reported magnetotactic behavior. This behavior is at least partially dependent on environmental oxidation-reduction potential. The co-existence of MTB with opposing polarities in the same redox environment conflicts with current models of the adaptive value of magnetotaxis.

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Thermodynamics of Fe oxides: Part II. Enthalpies of formation and relative stability of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and maghemite (γ-Fe₂O₃)

Cited by 150 publications

References 28 publications

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Pressure-temperature stability studies of FeOOH using X-ray diffraction

Geobiology of marine magnetotactic bacteria

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Thermodynamics of Fe oxides: Part II. Enthalpies of formation and relative stability of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and maghemite (γ-Fe2O3)

Cited by 150 publications

References 28 publications

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Modeling the iron oxides and oxyhydroxides for the prediction of environmentally sensitive phase transformations

Pressure-temperature stability studies of FeOOH using X-ray diffraction

Geobiology of marine magnetotactic bacteria

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Thermodynamics of Fe oxides: Part II. Enthalpies of formation and relative stability of goethite (α-FeOOH), lepidocrocite (γ-FeOOH), and maghemite (γ-Fe₂O₃)