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1.
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2.
57Fe Mössbauer spectra have been obtained from samples of humic acid, fulvic acid and kerogen and from the organic material extracted from bituminous chalk with benzene-methanol. The spectra indicate that iron occurs in a trivalent form in the silicate residue of the humic acid fraction, as hydrated ferrous ions associated with the fulvic acid fraction, as pyrite in kerogen and in a form not detectable by Mössbauer spectroscopy in the benzene-methanol extract.  相似文献   

3.
The Mössbauer spectra of one chromite at 298 K and one chromite at 298, 200, 170, 140 and 90 K have been analyzed in this study. A Voigt-based quadrupole splitting distribution (QSD) method was used to analyze the spectra. The tetrahedral site Fe2+ and the octahedral site Fe3+ quadrupole splitting distributions (QSDs) were obtained from the Mössbauer spectra of chromites, and the multiple tetrahedral site Fe2+ Gaussian QSD components and the large widths σ Δ of the Gaussian QSD components of the tetrahedral site Fe2+ QSDs for chromites were attributed to next-nearest neighbor effects. In addition, temperature dependences of the isomer shift and the quadrupole splitting were presented and discussed. Comparisons between the Mössbauer parameters for thickness-corrected folded spectra and raw-folded spectra of chromites were made, and the results show that the two sets of the Mössbauer parameters and ratios of ferric to total iron as well as χ2 are very close to each other. This is because of the small absorber thickness of chromites in this study. Comparisons between the Mössbauer parameters of chromites obtained using the Voigt-based QSD method and a Lorentzian doublet method were also made. The results show that there are some differences between the two sets of the Mössbauer parameters and ratios of ferric to total iron, but not significant. However, much larger χ2 were obtained when the Lorentzian doublet method was used to fit the spectra of chromites. This indicates that the Voigt-based QSD method is more adequate to analyze the Mössbauer spectra of chromites from the point of view of statistics.  相似文献   

4.
New data on the structure of Garfield nontronite have been produced by the use of different spectroscopic techniques: Mössbauer spectroscopy, optical spectroscopy, X-ray absorption edges and EXAFS and NMR. The tetrahedral iron content is found to be no higher than 1 percent. All iron atoms belong to the octahedral sheet excluding the possibility of the presence of non crystallized phases. Some ambiguities remain about the coherence of the octahedral sheet because of the presence of two doublets in the Mössbauer spectrum and at least two lineshapes in NMR spectra of OH which correspond to different environments.  相似文献   

5.
The Fe3+/Σ Fe of twenty-nine experimentally formed, iron-bearing silicate glasses has been determined by wet-chemical and Mössbauer spectroscopic methods from 5–10 mg individual splits of 20–40 mg experimental run products. The wet-chemical and Mössbauer analyses were conducted in two separate laboratories (University of California, Berkeley, and the Geophysical Laboratory, respectively). The Fe3+/Σ Fe ranges from less than 0.2 to 0.96, and the total iron oxide content of the samples, from 2.2 to 34.7 wt %, added as Fe2O3. The interlaboratory comparison shows 70% of the Fe3+/ΣFe analyses from the two methods within the quoted uncertainties (±1 σ) of each other and 83% of the analyses within ±2 σ of each other. Replicate analyses in the current data set result in variations within ±1 σ. These uncertainties are similar to those obtained from several hundred Fe3+/Σ Fe analyses of reequilibrated natural rock and simple system compositions carried out with identical analytical methods in the two laboratories. There is no systematic bias in the results from either of the two techniques. The Fe3+/Σ Fe of silicate glasses can be analyzed, therefore, with equal confidence by either the wet-chemical or the Mössbauer spectroscopic method.  相似文献   

6.
The phase and spin transitions in single-crystal monoclinic ferrosilite, FeSiO3, were investigated using X-ray diffraction and Mössbauer spectroscopy up to lower-mantle pressures and room temperature in a helium pressure medium. Using single-crystal X-ray diffraction, we measured the equation of state of ferrosilite up to about 43 GPa. We observed a P21/c-to-C2/c phase transition between 1.5 and 1.7 GPa and a phase transition from C2/c to a distinct P21/c structure between 30 and 34 GPa. With time-domain Mössbauer spectroscopy, we determined the hyperfine parameters of ferrous iron up to 95 GPa. The phase transitions were correlated with discontinuities in Mössbauer spectral features. We observed the onset of high-spin-to-low-spin transitions in the M1 and M2 sites at ～37 GPa and ～74 GPa, respectively. Understanding the electronic structure of iron in a well-characterized single crystal of ferrosilite may help interpret the behavior of iron in complex dense silicate phases.  相似文献   

7.
Iron (III) oxides are common constituents of geologic materials, they are products and by-products of many industrial processes, they are involved in biological processes, and they are the outcome of iron and steel corrosion. In many of these examples the iron oxides are — fortuitously or intentionally — of small particle size, and as a consequence difficult, if not impossible, to characterize by standard physicochemical techniques. 57Fe Mössbauer spectroscopy is suitable for this purpose because it can serve as a probe of the electric and magnetic conditions in the vicinity of iron nuclei in solid samples, no matter how the iron may be bound. Deviations of the magnetic properties of iron oxides of small particle size from those of their bulk counterparts lead to radical changes in the appearance of their Mössbauer spectra. Diverse models that have been put forward to account for such changes are discussed in this paper, including superparamagnetism, collective magnetic excitations, anomalous recoil-free fractions, superferromagnetism, spin canting and speromagnetism, reduced hyperfine field supertransfer, and Néel temperature reductions and distributions. Specific examples of microcrystalline iron (III) oxides and related minerals originating from different natural environments, resulting from technical processes, and being studied as planetary analogs are presented and discussed in the light of present-day knowledge on the properties of such materials.  相似文献   

8.
Practically identical Mössbauer spectra have been obtained for 40 ferromanganese nodules from a wide variety of marine and fresh-water locations. None of the nodules examined contains more than one weight percent Fe2+, so no more than a few percent of the total iron in these nodules can be Fe2+. Most of the iron is present as Fe3+ in paramagnetic or superparamagnetic oxide phases, although hysteresis loops show the presence of small amounts of ferromagnetic phases not detected by the Mössbauer technique.  相似文献   

9.
Mössbauer effect and magnetisation measurements show strong evidence that the principal form of native and introduced iron in Victorian brown coals is as isolated Fe3+ ions octahedrally coordinated to a range of oxygen-containing ligands. The mean iron-iron separation is less than expected from a uniform distribution, but there is strong evidence against clustering. All experimental evidence is consistent with these iron ions being located in the water bridges between the coal micelles. Although the Fe3+ ions remain paramagnetic down to 4.2 K, magnetic coupling between nearby Fe3+ ions causes slow paramagnetic relaxation in the low temperature Mössbauer spectra.  相似文献   

10.
57Fe Mössbauer spectra of iron bearing alumino-silicate glasses are analysed by two complementary methods (SID and x-VBF) especially adapted for the analysis of disordered systems by taking into account distributions of hyperfine Mössbauer parameters. Qualitative and quantitative information about the oxidation state of iron are obtained as well as information about the distribution of local environments of iron. The possibility to separate the signal of ferric iron from that of ferrous iron allows to derive precise redox ratio in favourable cases but also to analyse more sharply the different contributions to Mössbauer spectra. Using two different glass series (feldspar composition, haplo-tonalitic composition), the characteristics of the two methods are described and employed to study the effect of composition, water incorporation and oxidation state on the glass structure. Optical absorption spectroscopy is used to support the interpretation of the Mössbauer spectra in case of the feldspar glasses.  相似文献   

11.
Despite a large number of studies of iron spin state in silicate perovskite at high pressure and high temperature, there is still disagreement regarding the type and P–T conditions of the transition, and whether Fe2+ or Fe3+ or both iron cations are involved. Recently, our group published results of a Mössbauer spectroscopy study of the iron behaviour in (Mg,Fe)(Si,Al)O3 perovskite at pressures up to 110 GPa (McCammon et al. 2008), where we suggested stabilization of the intermediate spin state for 8- to 12-fold coordinated ferrous iron ([8–12]Fe2+) in silicate perovskite above 30 GPa. In order to explore the behaviour in related systems, we performed a comparative Mössbauer spectroscopic study of silicate perovskite (Fe0.12Mg0.88SiO3) and majorite (with two compositions—Fe0.18Mg0.82SiO3 and Fe0.11Mg0.88SiO3) at pressures up to 81 GPa in the temperature range 296–800 K, which was mainly motivated by the fact that the oxygen environment of ferrous iron in majorite is quite similar to that in silicate perovskite. The [8–12]Fe2+ component, dominating the Mössbauer spectra of majorites, shows high quadrupole splitting (QS) values, about 3.6 mm s?1, in the entire studied P–T region (pressures to 58 GPa and 296–800 K). Decrease of the QS of this component with temperature at constant pressure can be described by the Huggins model with the energy splitting between low-energy e g levels of [8–12]Fe2+ equal to 1,500 (50) cm?1 for Fe0.18Mg0.82SiO3 and to 1,680 (70) cm?1 for Fe0.11Mg0.88SiO3. In contrast, for the silicate perovskite dominating Mössbauer component associated with [8–12]Fe2+ suggests the gradual change of the electronic properties. Namely, an additional spectral component with central shift close to that for high-spin [8–12]Fe2+ and QS about 3.7 mm s?1 appeared at ~35 (2) GPa, and the amount of the component increases with both pressure and temperature. The temperature dependence of QS of the component cannot be described in the framework of the Huggins model. Observed differences in the high-pressure high-temperature behaviour of [8–12]Fe2+ in the silicate perovskite and majorite phases provide additional arguments in favour of the gradual high-spin—intermediate-spin crossover in lower mantle perovskite, previously reported by McCammon et al. (2008) and Lin et al. (2008).  相似文献   

12.
The first Mössbauer results obtained with powdered samples of natural wolframites Fe x Mn1?x WO4 from some famous Portuguese and Peruvian mines are reported here. The Mössbauer experiments have been carried out at 300, 77 and 4.2 K with four natural and one synthetic powdered samples of different compositions. The Mössbauer parameter values can be attributed to a high spin ferrous ion in a quite distorted octahedral symmetry. From the 4.2 K spectra, one deduces a weak value for the hyperfine magnetic field (H hf?45 kOe), a negative sign for the quadrupole interaction, and an approximate value for the asymmetry parameter (η?0.7). X-ray diffractometry experiments developed to determine the lattice constants have shown a linear behaviour of the most sensitive parameter a as a function of the iron content x. In parallel, a linear behaviour of the Néel temperature T N with x observed between x=0.5 and x=1.  相似文献   

13.
The influence on the spinel structure of Fe3+ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr2O4–MgFe2O4) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe2O4), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe3+ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a 0 and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe3+ at the M site on T–O bond lengths in the spinel structure.  相似文献   

14.
The iron-bearing phases in nodules from two regions (the Pacific Ocean — Clarion-Clipperton, and the Indian Ocean — Central plain) have been studied by Mössbauer Spectroscopy. The major compounds are established to be Fe(OH)3, (FeOOH·H2O) and FeCO3. The value of the recoilless absorption probability f′ is measured for Fe(OH)3. Meisel's method for quantitative determination of iron containing compounds has been adapted for the case of nodule samples. By taking into account the f′ values, the error of quantitative determination is considerably reduced. The Fe2+ distribution in the nonequivalent M1 and M2 positions of pyroxene has been studied. It is shown that the pyroxene crystals in the silicate material originated as a result of rapid cooling of the magma in ocean water.  相似文献   

15.
A combined polarized optical absorption and 57Fe Mössbauer spectroscopy study of inhomogeneous, Fe and Ti-bearing terrestrial hibonite (Madagascar) has been carried out. Mössbauer data were also obtained on synthetic material prepared under different fo2 inconditions. A strong band at 5400 cm-1 in the near-infrared spectra is attributed to spin-allowed d-d transitions of Fe2+ occupying tetrahedral sites within the spinel blocks of the hibonite crystal structure. There is agreement with the Mössbauer results, showing that ferrous iron orders onto a single, low-coordinated crystallographic site. Ferric iron is distributed over several positions, but shows strongest preference for the large bipyramidal site located outside the spinel blocks. The colour and pleochroism of hibonite in thin section is related to a prominent UV absorption edge, and several broad absorption bands in the visible spectrum ascribed to charge-transfer transitions involving Fe2+, Fe3+ and Ti4+.  相似文献   

16.
Analysis of 57Fe transmission Mössbauer spectra collected on a system where the proportional counter has been replaced with a silicon drift detector (SDD) to test milliprobing of mineral samples is described. In the region of the 14.4 keV Mössbauer line the detector has about 70% efficiency and is capable of delivering spectroscopic information with a high energy resolution and high counting rate. Satisfactory results are obtained from a phase analysis of mixtures of olivine and ilmenite in the proportion 97:3, 99:1 wt%, where in the latter case 2.4 μg of Fe3+ in the form of hematite was found in the ilmenite. New perovskite-type minerals (Pb1.33Ba0.67Fe2O5, Pb1.33Sr0.67Fe2O5 and Pb1.33Ba0.33Sr0.33Fe2O5), synthesised by a combustion method, were studied by X-ray diffraction and Mössbauer spectroscopy as well. The advantage of the system with SDD compared to a conventional Mössbauer spectrometer equipped with a proportional counter as a detector is demonstrated for the perovskite samples. The Mössbauer set-up with the silicon drift detector may be successfully used for a wide range of materials containing a negligible amount of iron.  相似文献   

17.
Isotopically anomalous Te is a by-product of the nuclear processes in zones of supernovae that have been proposed as sources for isotopically anomalous Xe. The calculated composition of the anomalous Te is roughly consistent with the disputed measurements made by Balladet al. (1979) and Oliveret al. (1979) of samples of the Allende meteorite with the exception that the large 123Te overabundance reported by Oliveret al. (1979) is not predicted by the theory.  相似文献   

18.
Mössbauer effect, (ME) and powder X-ray diffraction, (XRD) have been used to study the relationship between cationic size, tetrahedral layer rotation, octahedral layer flattening, stability, and Mössbauer quadrupole splitting, qs, of iron bearing trioctahedral micas. Tetrahedral layer rotation accounts for much of the lattice adjustment but biotites that require an angle of rotation higher than 21 degrees are not stable. Both experimental and computational data show that qs for Fe3+ (IV) increases with increasing degree of tetrahedral layer rotation. A systematic increase of qs for Fe2+ (VI) is also observed, but this could be due to factors other than tetrahedral layer rotation.  相似文献   

19.
Three natural lawsonites from Syke Rock, Mendocino Co., Reed Ranch, Marin Co., and Blake Gardens, Sonoma Co., all from the Coast Range Region in California, were studied by 57Fe Mössbauer spectroscopy, electron microprobe analysis, and X-ray powder diffraction. The samples contain about 0.6, 1.0, and 1.4 wt% of total iron oxide, respectively. 57Fe Mössbauer spectra are consistent with the assumption that high-spin Fe3+ substitutes for Al in the octahedrally coordinated site. The Mössbauer spectrum of lawsonite from Syke Rock exhibits a second doublet with 57Fe hyperfine parameters typical for octahedrally coordinated high-spin Fe2+. Electronic structure calculations in the local spin density approximation yield quadrupole splittings for Fe3+ in quantitative agreement with experiment indicating, however, that substitution of Al by Fe3+ must be accompanied by local distortion around the octahedral site. Model calculations also reproduce the room temperature hyperfine parameters of ferrous high-spin iron assuming the substitution of Ca by Fe2+. However, it cannot be excluded that Fe2+ may occupy a more asymmetric site within the microstructural cavity occupied by Ca and a H2O molecule.  相似文献   

20.
Natural sinhalites, MgAlBO4, from the Ratnapura District, Sri Lanka, and from Bodnar Quarry near Hamburg, Sussex Co., New Jersey, USA, have been characterized by 57Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine the oxidation state and site occupancy of iron in the sinhalite structure. The samples contain about 3.35 and 1.46 wt% of total iron oxide, respectively. The structure refinement is successful and reproduces the total iron content provided that the substitution of Mg2+ by Fe2+ on the M2 position only is assumed. The 57Fe Mössbauer spectra at 77, 293, 573 and 773 K can be resolved into two doublets with hyperfine parameters common for octahedrally coordinated high-spin Fe2+. There is no evidence for iron in the tetrahedral site. Electronic structure calculations in local spin density approximation yield hyperfine parameters for Fe2+ on the M2-site at 0, 293, 573 and 773 K in quantitative agreement with experiments. Calculated spectroscopic properties for Fe2+ on the M1-site are at variance with the experimental data and, thus, indicate that substitution of Al3+ by Fe2+, if occurring at all, must be accompanied by considerable local expansion and distortion of the M1-octahedron.  相似文献   

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