Showing papers in "Hyperfine Interactions in 1998"
TL;DR: In this paper, the relative fraction of each iron oxide can be accurately determined from the Mossbauer subspectral area and recoil-free fraction for each phase, at temperatures of 300K, 77K and 4K.
Abstract: For fundamental studies of the atmospheric corrosion of steel, it is useful to identify the iron oxide phases present in rust layers. The nine iron oxide phases, iron hydroxide (Fe(OH)2), iron trihydroxide (Fe(OH)3), goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), feroxyhite (δ-FeOOH), hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4) are among those which have been reported to be present in the corrosion coatings on steel. Each iron oxide phase is uniquely characterized by different hyperfine parameters from Mossbauer analysis, at temperatures of 300K, 77K and 4K. Many of these oxide phases can also be identified by use of Raman spectroscopy. The relative fraction of each iron oxide can be accurately determined from the Mossbauer subspectral area and recoil-free fraction of each phase. The different Mossbauer geometries also provide some depth dependent phase identification for corrosion layers present on the steel substrate. Micro-Raman spectroscopy can be used to uniquely identify each iron oxide phase to a high spatial resolution of about 1 µm.
534 citations
TL;DR: In this paper, a plot of cell parameters c versus the cell parameter a on which hematite-like materials do not fall on a single line but occupy an entire region that is bounded by hydrohematite-hematite and protohematitehematite lines was introduced.
Abstract: We have studied several synthetic hematite-like materials, produced via different reactions using various hydrothermal conditions and various temperatures of annealing in air, by bulk elemental analysis, weight loss measurements, scanning electron microscopy, powder X-ray diffraction, Mossbauer spectroscopy, and SQUID magnetometry. We conclude that hematite-like materials cannot be related to pure stoichiometric hematite via a single stoichiometric or physical parameter and that at least two degrees of freedom are required. This is most clearly seen when we introduce a plot of the cell parameter c versus the cell parameter a on which hematite-like materials do not fall on a single line but occupy an entire region that is bounded by hydrohematite-hematite and protohematite-hematite lines. A Morin transition boundary on this c-a plot separates a region where Morin transitions occur from a larger region where Morin transitions do not occur down to 4.2 K. Previous claims that particle size is the dominant factor controlling the Morin transition are understood in terms of correlations between stoichiometry and particle size that are produced at synthesis. Changing contents of incorporated molecular water and structural hydroxyls with associated cation vacancies have different characteristic effects on the crystal structure and move the sample coordinates in different directions on a c-a plot. It is also shown that an accessory sulphate content is adsorbed on the individual hematite crystallites and is not structurally incorporated. Mossbauer spectroscopy is used, as usual, to identify and characterize the spin structure. In addition, hyperfine field distributions from room temperature spectra, extracted by a new method, give a sensitive measure of sample conditions but not a unique one since several factors affect the extracted distributions in similar ways.
132 citations
TL;DR: Mossbauer spectroscopy is a powerful technique for the characterization of materials formed in the weathering environment as mentioned in this paper, however, it is often restricted to the determination of the oxidation state of iron and average structural site distortions.
Abstract: Mossbauer spectroscopy is a powerful technique for the characterization of materials formed in the weathering environment. Mossbauer studies of clay-sized phyllosilicates, however, are burdened with several problems: the samples are rarely monomineralic, they may be poor in iron, and only few iron-rich species order magnetically above 4.2 K. Site occupancies are difficult to determine, and cis and trans octahedral-OH site assignments are normally not possible. Unequivocal information that can be gained from such work thus is often restricted to the determination of the oxidation state of iron and average structural site distortions. Mossbauer data on iron oxides are generally more straightforward to interpret because these can be studied in the magnetically ordered state. A further asset of Mossbauer spectroscopy when studying iron oxides lies in its high sensitivity for magnetically ordered phases. Adverse effects ensuing from small particle size, interparticle interactions, non-stoichiometry and foreign-element substitution that often affect the Mossbauer parameters of iron oxides occurring in clays and soils can be at least partly offset by taking spectra at low temperatures.
105 citations
TL;DR: In this article, a systematic Mossbauer study of Maghemite γ-Fe2O3 and Al-substituted Maghemites γ-(Fe1−yAly) 2O3 was carried out and three series of samples with different morphological characteristics and aluminum contents were investigated.
Abstract: This paper reviews a systematic Mossbauer study of maghemite γ-Fe2O3 and Al-substituted maghemites γ-(Fe1−yAly)2O3. Three series of samples prepared from different methods and having different morphological characteristics and aluminum contents were investigated. It was found that both the cation distribution and the solubility limit depend on the preparation method, and no general conclusion in that respect could be inferred. From the temperature dependence of the hyperfine fields the exchange integrals could be calculated, and were found as: JAB= −25 K, JAA= −18 K, and JBB= −3 K. The hyperfine fields show a crossing in the vicinity of 300 K, for both substituted and unsubstituted samples, as a result of the relatively strong A–A interaction. The Curie temperatures were found to be in the range of 948–730 K, the lower value referring to the sample containing 22 mole% Al. The influence of maghemite on the Mossbauer spectra (MS) of magnetite was explored in some detail. It was demonstrated on the basis of the MS recorded for a variety of reference mixtures, that it is not possible to resolve the ferric A-site components due to maghemite and magnetite, even with the absorber subjected to a strong external field.
85 citations
TL;DR: Mossbauer spectra can reveal the extent of iron retention in silicate structures upon heating, the identity of iron oxides initially present or formed during the heating process and their transformations, and the character of the atmosphere under which heating was carried out as discussed by the authors.
Abstract: 57Fe Mossbauer spectroscopy reveals changes in iron valence and iron site geometry when clays and clay minerals are heated, and allows a distinction to be made between paramagnetic and magnetically ordered phases. Mossbauer spectra can thus reveal the extent of iron retention in silicate structures upon heating, the identity of iron oxides initially present or formed during the heating process and their transformations, and the character of the atmosphere under which heating was carried out. This makes Mossbauer spectroscopy the most effective tool for the characterization of changes induced by heating phyllosilicates and iron oxides.
83 citations
TL;DR: In this paper, the dispersion of γ-Fe2O3 particles in a polymer was investigated by Mossbauer spectroscopy with a longitudinal magnetic field of 60 kOe. Spin canting effects as a function of the mean particle size varying from 3 to 10 nm, the interparticle distance, and the temperature were reported.
Abstract: Dispersions of γ-Fe2O3 particles in a polymer were investigated by Mossbauer spectroscopy with a longitudinal magnetic field of 60 kOe. Spin canting effects as a function of the mean particle size varying from 3 to 10 nm, the interparticle distance, and the temperature are reported.
81 citations
TL;DR: The introductory paper of the 11th International Clay Conference (ICC '97), held in Ottawa, June 15-21, 1997, introduced the Symposium and Mossbauer spectroscopy to the non-expert as mentioned in this paper.
Abstract: This is the introductory paper of the Mossbauer Symposium of the 11th International Clay Conference (ICC '97), held in Ottawa, June 15–21, 1997. Its purpose is to introduce the Symposium and Mossbauer spectroscopy to the non-expert. We answer the questions: “What is Mossbauer spectroscopy and how does it work?”, “How is it particularly useful in clay and soil science?”, and “What are its limitations and why is it not more widespread as a technique?”. We start from the basics and describe all the physical and chemical concepts that are required to perform correct spectral analysis and interpretation in order to give a complete and up to date treatment so that one may appreciate and use published Mossbauer results. A complete bibliography, including electronic sources, is given.
78 citations
TL;DR: Mossbauer spectroscopy was used to characterize a Green Rust as a natural mineral for the first time as discussed by the authors. But the counter-anion species cannot be specified even though hyperfine parameters perfectly match values of synthetic samples.
Abstract: Mossbauer spectroscopy is used to characterize a Green Rust as a natural mineral for the first time. Samples are taken from a hydromorphic soil under the forest at Fougeres (Brittany, France) during spring season. Spectra are compared with those of synthetic Green Rusts (GRs), i.e. hydroxy-chloride, -sulphate, -carbonate and display one ferric and one or two ferrous sites. Fe(II)/Fe(III) abundances ratio cannot be attributed definitely to one of those stoichiometric compounds. Therefore, the counter-anion species cannot be specified even though hyperfine parameters perfectly match values of synthetic samples. The Fe(II)/Fe(III) ratio obtained from the Mossbauer spectra decreases with sampling depth. The "fougerite" originates likely from the reduction of deeper Fe(III)-mineral species by anoxic waterlogging.
62 citations
TL;DR: In this paper, the development of the new field of nuclear inelastic scattering is reviewed and the experimental technique and the variety of applications are illustrated by recent results obtained at the Nuclear Resonance beamline of the European Synchrotron Radiation Facility.
Abstract: The development of the new field of nuclear inelastic scattering is reviewed. The experimental technique and the variety of applications are illustrated by recent results obtained at the Nuclear Resonance beamline of the European Synchrotron Radiation Facility.
58 citations
TL;DR: In this paper, the authors used X-ray diffraction to characterize the crystal structure of green rusts by distinguishing green rust one and two from a pyroaurite-sjogrenite-like structure.
Abstract: Fe(II)--Fe(III) hydroxy-chloride, -sulphate and -carbonate were prepared by oxidation of a ferrous hydroxide precipitate in anion-containing aqueous solutions The compounds are characterized by monitoring the redox potential Eh and the pH of stochiometric suspension vs time with the appropriate concentration ratios X-ray diffraction allows us to characterize the crystal structure by distinguishing “green rust one” (GR1) from “green rust two” (GR2) Since green rusts (GRs) are of a pyroaurite-sjogrenite-like structure, ie, consisting of intercalated foreign anions and water molecules in the interlayers between the brucite-like layers of Fe(OH)2, their chemical formulae can be determined from the Mossbauer spectra Three quadrupole doublets are observed: D1 and D2 correspond to a ferrous state with isomershift IS of about 127 mm s-1 and quadrupole splittings QS of about 285 and 260 mm s-1, respectively, whereas D3 corresponds to a ferric state with IS and QS of about 04 mm s-1 The hyperfine parameters of these doublets are similar from one green rust to another but their intensity ratios vary considerably Finally, Eh and pH equilibrium diagrams of the Fe species in the presence of chloride, sulphate and carbonate anions contained within the water solution are drawn and the thermodynamic conditions of existence and degrees of oxidation of green rusts are discussed
46 citations
TL;DR: The Mossbauer spectra of pyroaurite-sjogrenite-type compounds (PTC) are discussed with reference to the crystal structure, cation order, and crystallite morphology.
Abstract: The Mossbauer spectra of pyroaurite-sjogrenite-type compounds (PTC) (layered anion exchangers) are discussed with reference to the crystal structure, cation order, and crystallite morphology. It is shown that cation-ordered layers are produced in the synthesis of carbonate and sulphate types of green rust. In contrast, synthetic and natural pyroaurite only occurs as disordered types. The redox chemistry of Fe(III) within the metal hydroxide layer is illustrated with examples of electrochemical oxidation and reversible reduction by boiling glycerol. The chemistry of iron in the interlayer is exemplified by the intercalation of Fe-cyanide complexes in hydrotalcite. This reaction may be used as a probe for the charge distribution in the interlayer.
TL;DR: In this paper, it was found that a simple irradiation of iron and steel with pulses of an excimer laser in air or nitrogen leads to a significant nitrogen take-up into the surface and to improvements in the surface properties.
Abstract: Nitriding of iron and steels is well known to improve hardness, wear and corrosion resistance of surfaces. Recently, it has been found that a simple irradiation of iron and steel with pulses of an excimer laser in air or nitrogen leads to a significant nitrogen take-up into the surface and to improvements in the surface properties. The mechanisms of the laser-nitriding process are not yet understood but the nitrification will be proved by several methods. Among these, Mossbauer spectroscopy is very powerful, especially when Conversion Electron and Conversion X-ray Mossbauer Spectroscopy (CEMS and CXMS) are applied simultaneously. Nevertheless, only a combination of methods gives a satisfying overview of the laser induced nitriding processes: Rutherford Backscattering Spectrometry (RBS) and Resonant Nuclear Reaction Analysis (RNRA) were also used to characterize the treated surfaces. First measurements show an increase of the hardness and the wear resistance with the number of pulses. From the results of the CEMS analyses this should be correlated with the increase in the fraction of the e-phase. This may be important for industrial applications.
TL;DR: Early techniques of making pottery can be investigated by 57Fe Mossbauer spectroscopy as mentioned in this paper, which is generally present in unpurified clays in concentrations of several percent, and during firing, the iron undergoes characteristic changes of its chemical and physical state, depending on the kiln atmosphere and on the maximum firing temperature reached.
Abstract: Early techniques of making pottery can be investigated by 57Fe Mossbauer spectroscopy. Iron is generally present in unpurified clays in concentrations of several percent. During firing, the iron undergoes characteristic changes of its chemical and physical state, depending on the kiln atmosphere and on the maximum firing temperature reached. These changes can be followed by Mossbauer spectroscopy. Firing techniques can often be reconstructed when spectra of laboratory and field fired samples are compared with those observed in ancient sherds.
TL;DR: In this paper, the magnetic properties of Fe nitrides have been reexamined by 57Fe Mossbauer spectroscopy, and the results showed that the NaCl-type FeN is an antiferromagnet and shows a surprisingly large hyperfine magnetic field of 49 T.
Abstract: Magnetic properties of Fe nitrides have been reexamined by 57Fe Mossbauer spectroscopy. Hyperfine magnetic fields for α″-Fe16N2, γ′-Fe4N, e-Fe3N, ζ-Fe2N, NaCl-type FeN and ZnS-type FeN have been determined at various temperatures. Although α′-, γ″-, and e-nitride are all ferromagnets, ζ-Fe2N is found to be an antiferromagnet below 9 K and ZnS-type FeN is non-magnetic at 4.2 K. Contrary to the ZnS-type FeN, the NaCl-type FeN is an antiferromagnet and shows a component with a surprisingly large hyperfine magnetic field of 49 T.
TL;DR: In this article, the relation between the intensity of the long-lived component of lifetime distribution of positron annihilation and the number of defects (elementary free volumes) was considered.
Abstract: Free volume effects are important for positronium formation, pick‐off annihilation and chemical reactions. In order to make the method of positron annihilation an effective technique for quantitative studies of molecular solids, for example polymers, the relation between the intensity of the long‐lived component of lifetime distribution of positron annihilation and the number of defects (elementary free volumes) was considered. The analysis assumes selective trapping of positrons and positronium in the defects of ordered and disordered (crystalline and amorphous) sites, respectively, the sizes of nonhomogeneities are assumed to be lower than positron diffusion length. The results on positronium annihilation in porous poly(phenylene oxide) allow one to estimate nontrapped positronium diffusion coefficient which is equal to \($$\). The relation between the positronium lifetime and effective size of free volume for large pores (effective radius \(\geqslant \) 1 nm) is considered. Experimental results were obtained using the CONTIN program; some comments on its application for calculations of size distribution of elementary free volumes in polymers are discussed.
TL;DR: Ball milling can be used to induce solid state reactions in a variety of technologies, including the activation of silicates, inorganic synthesis, and mechanical alloying as discussed by the authors, which is a powerful tool to study these processes.
Abstract: Ball milling can be used to induce solid state reactions in a variety of technologies, including the activation of silicates, inorganic synthesis, and mechanical alloying. Mossbauer spectroscopy is a powerful tool to study these processes. Some typical examples are discussed in this paper, concerning disordering, alloying, and simple chemical reactions. Many more industrial applications are possible, with ample opportunity for meaningful Mossbauer investigations.
TL;DR: Mossbauer spectroscopic studies of soils are generally centered around the characterization of Fe3+ oxides, making use of distinctive magnetic properties of the different oxides and the high sensitivity of the technique for magnetically ordered phases as mentioned in this paper.
Abstract: Mossbauer spectroscopic studies of soils are generally centered around the characterization of Fe3+ oxides, making use of distinctive magnetic properties of the different oxides and the high sensitivity of the technique for magnetically ordered phases Most work on clays and clay minerals, in contrast, focuses on the determination of the oxidation state of iron, iron structural site occupancies and distortions, and the transformations that take place during clay firing
TL;DR: In this paper, the corrosion products on steels exposed at two sites in Campeche, Mexico and one site at Kure Beach, USA, have been investigated to determine the extent to which different marine conditions and exposure times control the oxide formation.
Abstract: The corrosion products on steels exposed at two sites in Campeche, Mexico and one site at Kure Beach, USA, have been investigated to determine the extent to which different marine conditions and exposure times control the oxide formation. The corroded coupons were analyzed by Mossbauer, Raman and infrared spectroscopy as well as X‐ray diffraction, in order to completely identify the oxides and map their location in the corrosion coating. The coating compositions were determined by Mossbauer spectroscopy using a new parameter, the relative recoilless fraction (F-value) which gives the atomic fraction of iron in each oxide phase from the Mossbauer sub‐spectral areas. For short exposure times, less than three months, an amorphous oxyhydroxide was detected after which a predominance of lepidocrocite (γ-FeOOH), and akaganeite (β-FeOOH) were observed in the corrosion coatings with the fraction of the later phase increasing at sites with higher atmospheric chloride concentrations. The analysis also showed that small clusters of magnetite (Fe3O4), and maghemite (γ(Fe2O3), were seen in the micro-Raman spectra but were not always identified by Mossbauer spectroscopy. For longer exposure times, goethite (α-FeOOH), was also identified but little or no β-FeOOH was observed. It was determined by the Raman analysis that the corrosion products generally consisted of inner and outer layers. The protective layer, which acted as a barrier to slow further corrosion, consisted of the α-FeOOH and nano-sized γ-Fe2O3 phases and corresponded to the inner layer close to the steel substrate. The outer layer was formed from high γ-FeOOH and low α-FeOOH concentrations.
TL;DR: In this paper, the average particle size and the kinds of Fe2O3 phase obtained (α, γ or e) are strongly dependent of the temperature on the final heat treatment.
Abstract: Fe2O3 fine particles dispersed in a silica gel have been prepared by a new sol-gel method and characterized. Various samples have been studied by means of Mossbauer spectroscopy for temperatures ranging between 4.2 K and 300 K. The results show that the average particle size and the kinds of Fe2O3 phase obtained (α, γ or e) are strongly dependent of the temperature on the final heat treatment.
TL;DR: In this paper, an up-to-date overview of selected magnetic soils forming on four representative examples of mafic lithology is presented, dealing with selected magnetic regions forming on 4 representative examples.
Abstract: Tropical soils typically retain high amounts of iron oxides and some of them are magnetic, in the sense that their spontaneous magnetization σ > 1JT-1 kg-1 The two major orders forming on mafic domains, namely, dusky red Oxisol and Alfisol, generically referred to as terrae rossae, are the most representative magnetic soils and cover as much as 39%(∼330 000 km2 of the Brazilian land area In this paper, an up‐to‐date overview is presented, dealing with selected magnetic soils forming on four representative examples of mafic lithology Some aspects of their iron oxide mineralogy and field and laboratory methodologies of study are discussed
TL;DR: In this paper, the concepts leading to the application of synchrotron radiation to elastic and inelastic nuclear resonant scattering are discussed and the resulting new experimental techniques are compared to conventional Mossbauer spectroscopy.
Abstract: The concepts leading to the application of synchrotron radiation to elastic and inelastic nuclear resonant scattering are discussed. The resulting new experimental techniques are compared to conventional Mossbauer spectroscopy. A survey of situations that favor experiments with synchrotron radiation is offered.
TL;DR: In this paper, photo-induced effects have been detected by magnetic measurements, Mossbauer spectroscopy and reflectivity, and the LIESST effect has been achieved in the spin-crossover system [FexCo1-x(btr)2(NCS)2]·H2O.
Abstract: Photo‐induced effects have been detected by magnetic measurements, Mossbauer spectroscopy and reflectivity. The LIESST effect has been achieved in the spin‐crossover system [FexCo1-x(btr)2(NCS)2]·H2O. We investigated the purely photo‐induced magnetism of a Prussian Blue analogue Rb0.52Co[Fe(CN)6]0.84, 2.31 H2O, involving an optical electron transfer from FeII to CoIII. Inherent aspects of photomagnetic experiments are described: bulk and surface effects, magnetic and electronic metastabilities of the photo‐excited state.
TL;DR: In this paper, a status report of the experiment PVLAS, whose aim is the measurement of the Polarization of Vacuum, induced by a high magnetic field, is given.
Abstract: The following is a status report of the experiment PVLAS, whose aim is the measurement of the Polarization of Vacuum, induced by a high magnetic field It includes a detailed description of the experimental set-up, in which a superconducting dipole magnet of more than 8 T, and a Fabry-Perot optical interferometer with a finesse of more than 130,000 are used The experiment is in progress at the Laboratori Nazionali di Legnaro in Italy
TL;DR: In this article, collision induced dissociation was applied to study the fragmentation channels of multiply charged gold clusters, Au N2+, size N= 7 -35, and Au> N3+}, N = 19 -35.
Abstract: Collision induced dissociation is applied to study the fragmentation channels of multiply charged gold clusters, Au N2+, size N= 7 –35, and Au> N3+}, N = 19–35, stored in an ion cyclotron resonance (Penning) trap. The main dissociation pathways are neutral monomer evaporation, Au> NZ+to Au> N-1Z+} + Au, for the larger and fission into a charged trimer plus the remaining cluster, Au> NZ+to{}Au> N-3(Z-1)+} +{}Au> 3+}, for the smaller clusters. In the intermediate cluster size region an odd–even alternation of the two competing decay pathways is observed. In addition, for some specific cluster sizes there are indications of neutral dimer evaporation, Au> NZ+to{}Au> N-2Z++Au> 2}, and of extremely asymmetric fission of the form Au> NZ+to Au> N-1(Z-1)+} + Au+.
TL;DR: In this paper, a single hydrogen-like ion (C5+) is prepared, cooled with the method of resistive cooling and non-destructively detected with the image-current technique in a cryogenic Penning trap at T = 4 K.
Abstract: We describe how a single hydrogen-like ion (C5+) is prepared, cooled with the method of resistive cooling and non-destructively detected with the image-current technique in a cryogenic Penning trap at T = 4 K. The storage time for C5+-ions in the cryogenically pumped vacuum chamber is longer than six months. The experimental techniques of preparing, cooling and detecting highly-charged ions in a Penning trap are relevant for precision experiments such as g-factor measurements, mass spectroscopy and laser spectroscopy.
TL;DR: In this paper, the Mossbauer spectra were evaluated in terms of quadrupole splitting distributions (QSDs) using three generalized sites for 〈Fe3+〉, [Fe3+,] and [Fe2].
Abstract: Trioctahedral potassium micas |K}[M3]〈T4〉O10(OH)2 have been synthesized by hydrothermal techniques with various cationic substitutions in the octahedral and the tetrahedral sheet. Taking annite |K}[Fe32+]〈AlSi3〉O10(OH)2 as the reference mineral, [Fe2] was replaced by [Mg2] and [Ni2], 〈Al3+〉 by 〈Fe3+〉 and finally [Fe2+] + 〈Si4+〉 by [Al3+] + 〈Al3+〉. Mossbauer spectra were evaluated in terms of quadrupole splitting distributions (QSDs) using three generalized sites for 〈Fe3+〉, [Fe3+] and [Fe2]. Annites, nominally free of 〈Fe3+〉, show a lower limit of [Fe3+]/Fetot of 0.10, which stabilizes the structure. The ferrous iron, [Fe2], QSD consists of two main components. In some of the solid solution series, there is strong experimental evidence for a third ferrous component, particularly at higher [Al3+] contents. This third component is centered at low quadrupole splittings and may be assigned to a defect [Fe2] site, forming 1:2 structures with two neighbouring trivalent octahedral cations. For charge compensation one OH− is replaced by O2− for each [M3+] cation. The ferrous QSDs vary systematically with chemical composition. Compared to those of annite, the QSD parameters (mean quadrupole splitting 〈QS〉 and quadrupole splitting with maximum probability, QSpeak) are shifted towards higher values with increasing [Mg2] and [Ni2] contents, and decrease slightly with increasing content of trivalent cations. These trends can be interpreted in terms of changes in the local environment around the Fe probe nucleus, i.e., in terms of decreasing or increasing distortions from the ideal octahedral configurations.
TL;DR: In this paper, the authors measured the Mossbauer spectra of three different samples of the Jilin meteorite at 78 and 295 K and identified five iron components, two magnetic components, kamacite and troilite, and three non-magnetic components, olivine, pyroxene, and an iron(III) component.
Abstract: The iron‐57 Mossbauer spectra of three different samples of the Jilin meteorite have been measured at 78 and 295 K. Five iron containing major components are identified, two magnetic components, kamacite and troilite, and three non‐magnetic components, olivine, pyroxene, and an iron(III) component. The relative absorption areas of these five components show that sample A contains a larger fraction of magnetic components, ca. 50 percent, than samples B and C, which contain ca. 30 percent. This difference indicates a significant compositional inhomogeneity in the Jilin meteorite. The fit of the troilite component sextet is extensively discussed in the paper and requires the adjustment of not only the isomer shift and hyperfine field, but also of the quadrupole interaction, the asymmetry parameter of the electric field gradient tensor, and the orientation of the hyperfine field in the principal axes of the electric field gradient tensor. The smaller isomer shift and hyperfine field of the kamacite mineral in sample B indicate that this sample contains less nickel than the kamacite in samples A and C, in which the amount of nickel is estimated to be ca. 9 percent. On the basis of its hyperfine parameters, the iron(III) component is assigned to iron(III) substituted on the M1 site of pyroxene.
TL;DR: In this paper, the authors compared the accuracy and precision of the Pratt and Wilson wet chemical (WC) methods and the Mossbauer spectroscopy (MS) method for ferric/ferrous determinations in mica granules and powders.
Abstract: We compare ferric/ferrous determinations in mica granules and powders, as obtained by the Pratt and Wilson wet chemical (WC) methods and by Mossbauer spectroscopy (MS). The Pratt method is accurate whereas the Wilson method is not but both have the same precision (σ = 1.2 wt.% FeO). Assuming that the Pratt WC method gave accurate ferric/ferrous ratios leads to a calculated ferric/ferrous ratio of MS recoilless fractions at room temperature for a given biotite sample of f
3+/f
2+ = 1.009(5). Also, the Mica-Fe and Mica-Mg international standards are shown to be unsuitable, with significant size-fraction dependencies of their oxidation states. These results are discussed in the general context of evaluating accuracy and precision of WC methods by comparisons with MS and of the special problems related to accuracy and precision with MS itself.
TL;DR: In this article, the results strongly suggest the neo-formation of magnetite/maghemite in the soils of Huangling (China) using 57Fe Mossbauer spectroscopy.
Abstract: Samples of four different loess/paleosol couplets of a loess sequence in Huangling (China) have been studied with 57Fe Mossbauer spectroscopy. Each sample was separated into strongly, weakly and very weakly magnetic fractions. The iron mineralogy of the strongly magnetic fractions of both loess and soils consists of magnetite/maghemite and hematite together with some silicates. The soils contain some additional small-particle maghemite. From the spectral behaviour a similarity in terms of morphology and crystal chemistry for hematite throughout the whole section could be inferred. The ratio of iron in magnetite and maghemite to that in hematite differentiates well between the loess and soil samples. These results strongly suggest the neo-formation of magnetite/maghemite in the soils.
TL;DR: In this paper, the authors used a recently published method for the renormalization of the self-energy to calculate the self energy of 6s and 8d levels to all orders in Zα.
Abstract: We use a recently published method for the renormalization of the self-energy to calculate the self-energy of 6s and 8d levels to all orders in Zα. We demonstrate the accuracy of the method and its potential for high-n, low-Z applications. We also show that this method is perfectly suited for the evaluation of the two-electron self-energy (self-energy screening). For the first time, evaluation of the screening of the 1s electron by a second one in either the 1s,2s, 2p1/2 or 2p3/2 shells has been performed, for 30 ⩽ Z ⩽92.