Mössbauer studies of some sulphide minerals

Vaughan, David J.; Ridout, M. S.

doi:10.1016/0022-1902(71)80472-4

Cited by 147 publications

(95 citation statements)

References 9 publications

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“…[49][50][51] The calculated electronic density of states (DOS) (Figure 1(b)) shows metallic character, with the electronic states of the Fe d-orbitals dominating the regions around the Fermi level, in agreement with the metallic nature deduced by Vaughan and Ridout. 53 These features are consistent with earlier DFT results of mackinawite. [54][55][56] The (001), (011), and (111) surfaces, which are the dominant growth surface FeS, 34,57 were created from the relaxed bulk material using the METADISE code, 58 which not only considers periodicity in the plane direction but also provides the different atomic layer stacking resulting in a zero dipole moment perpendicular to the surface plane, as is required for reliable and realistic surface calculations.…”

Section: Computational Detailssupporting

confidence: 91%

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

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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)

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Section: Computational Detailssupporting

confidence: 91%

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

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“…An electrical conductivity for mackinawite is not available, but the mineral has been considered to be metallic (i.e., highly delocalized Fe 3d electrons) based on its short Fe-Fe distance (2.60 Å), which is close to that in elemental iron (2.48 Å for α-iron). Mössbauer spectroscopy indicates that mackinawite has no magnetic ordering down to 4.2 K. 17,18 The spectra exhibit one singlet without quadrupole splitting and hyperfine coupling (isomer shift 0.2 mms -1 with respect to elemental iron) between room temperature and 4.2 K, and application of high magnetic fields (3 T) does not reveal an internal field contribution from electrons. This temperature-independent Mössbauer behavior along with the short Fe-Fe distance lead one to hypothesize that mackinawite is only Pauli paramagnetic.…”

Section: Mackinawite (Tetragonal Fes)mentioning

confidence: 99%

Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations

et al. 2011

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Mackinawite is a naturally-occurring layer type FeS mineral well-known to be important in biogeochemical cycles and, more recently, to the development of microbial fuel cells.Conflicting results have been published as to the magnetic properties of this mineral, with Mössbauer spectroscopy indicating no magnetic ordering and density functional theory predicting an antiferromagnetic ground state, similar to the Fe-based high-temperature superconductors with which it is isostructural and for which it is known that magnetism is suppressed by strong itinerant spin fluctuations. We investigated this latter possibility for mackinawite using photoemission spectroscopy (PES), near-edge X-ray absorption fine structure spectroscopy (XAS), and density functional theory (DFT) computations. Our Fe 3s core-level PES spectrum of mackinawite showed a clear exchange-energy splitting (2.9 eV) consistent with a 1 µ B magnetic moment on the Fe ions, while the Fe L-edge XAS spectrum indicated rather delocalized Fe 3d electrons in mackinawite similar to those in Fe metal. DFT computations demonstrated that the ground state of mackinawite is single-stripe antiferromagnetic, with an Fe magnetic moment (2.7 µ B ) that is significantly larger than the experimental estimate and has a strong dependence on the S height and lattice parameters. All of these trends signal the existence of strong itinerant spin fluctuations. If strong spin fluctuations are the mediators of electron pairing in these Fe-based superconductors, we conjecture that mackinawite may be one of the simplest Fe-based superconductors.

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“…1a). In the past, expansion along the c axis of crystalline mackinawite was explained by excess cation uptake between S-S layers (Vaughan and Ridout, 1971). It was also suggested that water molecules can be incorporated between the tetrahedral sheets (Wolthers et al, 2003) or that the expansion may be caused by lattice relaxation due to the small crystallite size (Rickard and Luther, 2007).…”

Section: Introductionmentioning

confidence: 99%

Structural properties and transformations of precipitated FeS

et al. 2012

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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...

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Mössbauer studies of some sulphide minerals

Cited by 147 publications

References 9 publications

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

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

Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations

Structural properties and transformations of precipitated FeS

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