Transformation of mackinawite to greigite; an in situ X-ray powder diffraction and transmission electron microscope study

Lennie, Alistair R.; Redfern, Simon A. T.; Champness, P. E.; Stoddart, Chris P.; Schofield, P. F.; Vaughan, David J.

doi:10.2138/am-1997-3-408

Cited by 152 publications

(135 citation statements)

References 27 publications

Supporting

Mentioning

123

Contrasting

Order By: Relevance

“…Even though we tried to ensure fully anoxic conditions during sample storage, transfer and analyses, the complete exclusion of oxygen was probably not achieved and we believe that in our dry-stored samples the fast transition to greigite was caused by air exposure. Dry conversions of mackinawite to greigite were previously reported in controlled oxidation experiments (Lennie et al, 1997;Boursiquot et al, 2001), and also in magnetosomes from magnetotactic bacteria (Pósfai et al, 1998), where the transformation was attributed to uncontrolled oxidation by air during specimen handling. The transformation in the dry powder samples proceeded faster than in the solution-aged, ambient-temperature samples because the starting material was crystalline mackinawite instead of poorly ordered FeS am , facilitating the solid-state conversion from mackinawite and greigite.…”

Section: Dry Transformation Of Mackinawite Into Greigitementioning

confidence: 56%

“…Spacings that are significantly larger than d (001) in crystalline mackinawite are designated by asterisks (RT: room temperature, XRD: X-ray powder diffraction, TEM: transmission electron microscopy, TMS: transmission Mössbauer spectroscopy, XPS: X-ray photoelectron spectroscopy, PDF: pair distribution analysis, SEM: scanning electron microscopy, LAXRD: low-angle X-ray powder diffraction, HRTEM: high-resolution transmission electron microscopy, XAS: X-ray absorption spectroscopy, SAED: selected-area electron diffraction). (Lennie et al, 1997;Pósfai et al, 1998;Boursiquot et al, 2001), with the preservation of the cubic close-packed sulfide substructure that is the same in mackinawite and greigite ( Fig. 1).…”

Section: Introductionmentioning

confidence: 85%

“…Although in some cases the initial iron sulfide precipitate was reported to contain greigite alongside mackinawite (Watson et al, 2000;Gramp et al, 2010), it is generally assumed that greigite does not form directly from solution but converts from the pre-existing mackinawite (Hunger and Benning, 2007). The phase transition requires the oxidation of iron and either the addition of sulfur or loss of iron (Horiuchi, 1971;Lennie et al, 1997). Under anhydrous conditions, Lennie et al, 1995Skinner et al, 1964De Villiers and Liles, 2010Skála et al, 2006 a Cell parameters for 6C pyrrhotite.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structural properties and transformations of precipitated FeS

et al. 2012

View full text Add to dashboard Cite

Editor: J. Fein Keywords:Amorphous iron sulfide Mackinawite Greigite Phase transformations XRD TEM Nanocrystalline iron sulfides form in diverse anoxic environments. The initial precipitate is commonly referred to as nanocrystalline mackinawite (FeS) or amorphous FeS. In order to better understand the structure of the initial precipitate and its conversion to mackinawite and greigite (Fe 3 S 4 ), we studied synthetic iron sulfide samples that were precipitated from hydrous solutions near room temperature. The transformation of precipitated FeS was followed in both aqueous and dry aging experiments using X-ray powder diffraction (XRD) and scanning and transmission electron microscopy (SEM/TEM) and selected-area electron diffraction (SAED). Under tightly controlled anoxic conditions the first precipitate was nanocrystalline mackinawite. In contrast, when anaerobic conditions during synthesis were not completely ensured, freshly precipitated iron sulfide was typically X-ray amorphous (FeS am ), and showed only one broad Bragg-peak at 2Θ = 16.5°(5.4 Å). A distribution of interatomic distances calculated from pair-distribution function analysis of SAED patterns of FeS am showed that only short-range (b 7 Å) order was present in the bulk of the material, with Fe mainly present in tetrahedral coordination. SEM and TEM images confirmed the poorly ordered structure and showed that FeS am formed aggregates of curved, amorphous sheets that contained 3-8 structurally ordered layers at their cores. Such layers are generally assumed to be structurally similar to the tetrahedral iron sulfide layers in mackinawite. However, both inter-and intralayer spacings measured in high-resolution TEM images (~5.3 to 6.3 and~3.0 to 3.1 Å, respectively) were significantly larger than the corresponding spacings in crystalline mackinawite (5.03 and 2.6 Å, respectively), suggesting that short-range structural order within the semi-ordered layers of FeS am was not mackinawite-like. In aqueous aging experiments at room temperature, FeS am transformed into a mixture of mackinawite and greigite in~2 months, and completely converted to platy greigite crystals after~10 months. These aqueous transformations were likely driven by excess sulfur in the reacting solutions. We also studied the conversions of nanocrystalline mackinawite. In order to accelerate phase transitions, the initial FeS precipitate was heated to 120°C, resulting in the formation of crystalline mackinawite within 2 h; at 150°C, the material converted directly to pyrrhotite. Finally, when stored in a dry state at room temperature, crystalline mackinawite converted to greigite in 3 months, much faster than in the equivalent experiments in the aqueous solution, probably as a result of a more oxidative environment. The distinction between FeS am and nanocrystalline mackinawite is significant, since conditions for the formation of both phases are present in natural settings. Our experiments in a well-sealed anaerobic chamber simulate iron sulfide formation under anoxic conditions, where...

show abstract

Section: Dry Transformation Of Mackinawite Into Greigitementioning

confidence: 56%

Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Structural properties and transformations of precipitated FeS

et al. 2012

View full text Add to dashboard Cite

show abstract

“…[49][50][51] Moreover, both room temperature neutron diffraction 52 and Mössbauer data 53 at 4.2 K with an external field testify to the absence of an iron magnetic moment in mackinawite. In earlier studies, we have demonstrated that the inclusion of dispersion corrections yields improved agreement between the predicted lattice parameters (a = 3.587 Å, c = 4.908 Å, and c/a = 1.368) 33,34 and those measured experimentally.…”

Section: Computational Detailsmentioning

confidence: 89%

Activation and dissociation of CO2 on the (001), (011), and (111) surfaces of mackinawite (FeS): A dispersion-corrected DFT study

Dzade

Roldan

Leeuw

2015

The Journal of Chemical Physics

View full text Add to dashboard Cite

Iron sulfide minerals, including mackinawite (FeS), are relevant in origin of life theories, due to their potential catalytic activity towards the reduction and conversion of carbon dioxide (CO 2 ) to organic molecules, which may be applicable to the production of liquid fuels and commodity chemicals. However, the fundamental understanding of CO 2 adsorption, activation, and dissociation on FeS surfaces remains incomplete. Here, we have used density functional theory calculations, corrected for long-range dispersion interactions (DFT-D2), to explore various adsorption sites and configurations for CO 2 on the low-index mackinawite (001), (110), and (111) surfaces. We found that the CO 2 molecule physisorbs weakly on the energetically most stable (001) surface but adsorbs relatively strongly on the (011) and (111) FeS surfaces, preferentially at Fe sites. The adsorption of the CO 2 on the (011) and (111) surfaces is shown to be characterized by significant charge transfer from surface Fe species to the CO 2 molecule, which causes a large structural transformation in the molecule (i.e., forming a negatively charged bent CO 2 −δ species, with weaker C-O confirmed via vibrational frequency analyses). We have also analyzed the pathways for CO 2 reduction to CO and O on the mackinawite (011) and (111) surfaces. CO 2 dissociation is calculated to be slightly endothermic relative to the associatively adsorbed states, with relatively large activation energy barriers of 1.25 eV and 0.72 eV on the (011) and (111)

show abstract

“…Because structural characterization of these iron sulfide phases is limited 9,11 and remains controversial, as mentioned above, structural optimization using VASP was first conducted on a hypothetical, stoichiometric, tetragonal "FeS" as a benchmark for investigation of Fe 1+x S. Stoichiometric "FeS". The lattice parameters, a = 3.679 Å, c = 5.047 Å, and atomic positions originally reported by Berner were used as the starting point for VASP optimizations even though the original report noted the presence of excess iron.…”

Section: Composition and Bonding In Tetragonal Iron Sulfidesmentioning

confidence: 99%

Validation of Interstitial Iron and Consequences of Nonstoichiometry in Mackinawite (Fe_1+xS)

Brgoch

Miller

2012

J. Phys. Chem. A

View full text Add to dashboard Cite

A theoretical investigation of the relationship between chemical composition and electronic structure was performed on the nonstoichiometric iron sulfide, mackinawite (Fe 1+x S), which is isostructural and isoelectronic with the superconducting Fe 1+x Se and Fe 1+x (Te 1-y Se y ) phases. Even though Fe 1+x S has not been measured for superconductivity, the effects of stoichiometry on transport properties and electronic structure in all of these iron-excess chalcogenide compounds has been largely overlooked. In mackinawite, the amount of Fe that has been reported ranges from a large excess, Fe 1.15 S, to nearly stoichiometric, Fe 1.00 (7) S. Here, we analyze, for the first time, the electronic structure of Fe 1+x S to justify these nonstoichiometric phases. First principles electronic structure calculations using supercells of Fe 1+x S yield a wide range of energetically favorable compositions (0 < x < 0.30). The incorporation of interstitial Fe atoms originates from a delicate balance between the Madelung energy and the occupation of Fe-S and Fe-Fe antibonding orbitals. A theoretical assessment of various magnetic structures for "FeS" and Fe 1.06 S indicate that striped magnetic ordering along [110] is the lowest energy structure and the interstitial Fe affects the values of moments in the square planes as a function of distance. Moreover, the formation of the magnetic moment is dependent on the unit cell volume, thus relating it to composition. Finally, changes in the composition cause a modification of the Fermi surface and ultimately the loss of a nested vector. ABSTRACT: A theoretical investigation of the relationship between chemical composition and electronic structure was performed on the nonstoichiometric iron sulfide, mackinawite (Fe 1+x S), which is isostructural and isoelectronic with the superconducting Fe 1+x Se and Fe 1+x (Te 1−y Se y ) phases. Even though Fe 1+x S has not been measured for superconductivity, the effects of stoichiometry on transport properties and electronic structure in all of these iron-excess chalcogenide compounds has been largely overlooked. In mackinawite, the amount of Fe that has been reported ranges from a large excess, Fe 1.15 S, to nearly stoichiometric, Fe 1.00 (7) S. Here, we analyze, for the first time, the electronic structure of Fe 1+x S to justify these nonstoichiometric phases. First principles electronic structure calculations using supercells of Fe 1+x S yield a wide range of energetically favorable compositions (0 < x < 0.30). The incorporation of interstitial Fe atoms originates from a delicate balance between the Madelung energy and the occupation of Fe−S and Fe−Fe antibonding orbitals. A theoretical assessment of various magnetic structures for "FeS" and Fe 1.06 S indicate that striped magnetic ordering along [110] is the lowest energy structure and the interstitial Fe affects the values of moments in the square planes as a function of distance. Moreover, the formation of the magnetic moment is dependent on the unit cell volume, thus relating it to...

show abstract

Transformation of mackinawite to greigite; an in situ X-ray powder diffraction and transmission electron microscope study

Cited by 152 publications

References 27 publications

Structural properties and transformations of precipitated FeS

Structural properties and transformations of precipitated FeS

Activation and dissociation of CO2 on the (001), (011), and (111) surfaces of mackinawite (FeS): A dispersion-corrected DFT study

Validation of Interstitial Iron and Consequences of Nonstoichiometry in Mackinawite (Fe_1+xS)

Contact Info

Product

Resources

About

Transformation of mackinawite to greigite; an in situ X-ray powder diffraction and transmission electron microscope study

Cited by 152 publications

References 27 publications

Structural properties and transformations of precipitated FeS

Structural properties and transformations of precipitated FeS

Activation and dissociation of CO2 on the (001), (011), and (111) surfaces of mackinawite (FeS): A dispersion-corrected DFT study

Validation of Interstitial Iron and Consequences of Nonstoichiometry in Mackinawite (Fe1+xS)

Contact Info

Product

Resources

About

Validation of Interstitial Iron and Consequences of Nonstoichiometry in Mackinawite (Fe_1+xS)