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Thermally-induced reductive decomposition of natural iron-bearing garnets of the almandine-pyrope and almandine-spessartine series were studied at temperatures up to 1200 °C (heating rate of 10 °C/min) under atmosphere of forming gas (10% of H2 in N2). Crystallochemical formula of the studied garnet was calculated as VIII(A3−xFex2+)VI(Al,Fe3+)2Si3O12, where the amount of Fe3+ in the octahedral sites is negligible with the exception of pyrope, A = Mg, Mn, and 0.47 ≤ x ≤ 2.85. The observed decomposition temperature, determined from differential scanning calorimetry and thermogravimetry, is greater than 1000 °C in all cases and showed almost linear dependence on the iron content in the dodecahedral sites of the studied garnets, with the exception of garnet with a near-pyrope composition (Prp80Alm20). The initial garnet samples and decomposition products were characterized in details by means of X-ray powder diffraction and 57Fe Mossbauer spectroscopy. We found that all studied garnets have common decompositi...

To date, iron oxides have become one of the most studied nanomaterials due to their interesting and aaplication appealing physical, chemical, and biological properties in comparison with their bulk counterparts. In general, four forms of iron(III) oxide can be distinguished depending on their crystallographic and magnetic properties. In this work, one of the rare phases of iron(III) oxide, β‐Fe2O3, prepared by the solid state reaction was explored for the thermal transformations in various ambient atmospheres, including O2, N2, and CO2 atmospheres. The thermally treated products were investigated employing X-ray powder diffraction and 57Fe Mossbauer spectroscopy.

Powdered troilite (FeS), extracted from the Cape York IIIA octahedrite meteorite, was investigated employing in-field 57Fe Mossbauer spectroscopy. The study identified a typical behavior of polycrystalline antiferromagnetic material under external magnetic fields. The in-field evolution of the 57Fe Mossbauer spectra showed that the spin-flop transition in the FeS system occurs at a field higher than 5 T.

Oxidation of organosulfur compounds (S) by ferrate(VI) (FeVIO42−,Fe(VI)) proceeds by the transfer of oxygen atom to S. A vast amount of literature proposed oxygen atom transfer (OAT) via 2-e− transfer process in which Fe(IV) acts as an intermediate, and Fe(II) was also proposed to be an intermediate or final reduced iron species of Fe(VI)(FeVI→FeIV→FeII). In this paper, Mossbauer spectroscopy was applied to explore intermediate iron species in the oxidation of cysteine (Cys) and methionine (Met) by Fe(VI). In the oxidation of Cys, both Fe(II) and Fe(III) were observed while only Fe(III) was seen in the oxidation of Met by Fe(VI). These results support that no Fe(II) species was formed in the oxidation of Met before forming Fe(III). These results are in consistency with the possibility of initial 1-e− transfer with the formation of Fe(V) species and subsequent 2-e− transfer to yield Fe(III)(FeVI→FeV→FeIII).Oxidation of organosulfur compounds (S) by ferrate(VI) (FeVIO42−,Fe(VI)) proceeds by the transfer of oxygen atom to S. A vast amount of literature proposed oxygen atom transfer (OAT) via 2-e− transfer process in which Fe(IV) acts as an intermediate, and Fe(II) was also proposed to be an intermediate or final reduced iron species of Fe(VI)(FeVI→FeIV→FeII). In this paper, Mossbauer spectroscopy was applied to explore intermediate iron species in the oxidation of cysteine (Cys) and methionine (Met) by Fe(VI). In the oxidation of Cys, both Fe(II) and Fe(III) were observed while only Fe(III) was seen in the oxidation of Met by Fe(VI). These results support that no Fe(II) species was formed in the oxidation of Met before forming Fe(III). These results are in consistency with the possibility of initial 1-e− transfer with the formation of Fe(V) species and subsequent 2-e− transfer to yield Fe(III)(FeVI→FeV→FeIII).

Two isomorphous series Cu3SnS4−Cu2FeSnS4 (kuramite–stannite) and Cu2FeSnS4−Cu2ZnFeSnS4 (stannite–kesterite) have been studied by 57Fe and 119Sn Mossbauer spectroscopy. It has been found for the first series that at the Fe atom concentration below x0 = 0.45±0.02, iron atoms are only in the trivalent state and the concentration of Fe3+ and Cu1+ increases with an increase in x. The following scheme of isomorphous substitution of Cu for Fe may be proposed for this range of concentration: 2Cu2+(Td)→Cu1+(Td)+Fe3+(Oh). When x exceeds the boundary value x0, the Fe2+ ions appear. In the concentration range 0.45

An entirely new Mossbauer spectrometer MsAa‐4 is currently being under design and construction. New features as compared to the basic features of the previous generation MsAa‐3 spectrometer could be summarized as follows. Completely digital processing of the γ‐ray detector signal beyond the Gaussian shape filter/amplifier is to be implemented. The spectrometer is going to be able to accommodate external multiple detector heads. Up to 128 γ‐ray spectra in 16384 channels of 32‐bit each and up to 512 Mossbauer spectra in 4096 channels of 32‐bit each could be collected simultaneously, provided the proper external multiple detector head is used. The count‐rate per single detector is limited to about 105 counts per second in total. Improved precision of the reference function from 12‐bit to 16‐bit is to be provided. The reference function is stored in 8192 channels per a complete cycle. Addition of the random noise to the reference corner prism of the Michelson‐Morley calibration interferometer is to be introdu...

Present research is focused on tracing the oxidation of Al‐coated and Al2O3‐coated Fe powders with respect to their initial microstructure. The Mechanofusion process (MF) and the Fluidized‐Bed Metal Organic Chemical Vapour Deposition (FB‐MOCVD) techniques have been used to coat Fe particles respectively with Al2O3 and Al shell, respectively. Characterization of the as‐prepared and oxidized materials was performed by RT Mossbauer spectroscopy, XRD and SEM. Mossbauer spectroscopy shows quite pronounced differences both in the initial structure of Al‐coated and Al2O3‐coated Fe particles and also after their oxidation.

We have studied Verwey transition in NbxFe(3−2x)O4, which is prepared by solid state reaction at 1000 °C. A careful investigation on the influence of Nb5+ in niobium magnetite was carried out by both Mossbauer Effect (ME) and AC susceptibility measurements as a function of the temperature. A reduction transition temperature Tv in the range 97

This review article is intended to help all those, who now begin to work in the field of conversion electron Mossbauer spectroscopy (CEMS) and who have to select a right type of a detector. There exist a large number of specific engineering designs in each of the detector kind, which is impossible to cover in one paper. That is why we only try to outline basic classification and general survey of properties of individual CEMS detector kinds supplemented by references to its more detailed analysis. 57Fe is the most frequently used isotope in CEMS and thereby the paper is devoted to this case.

Aluminium based rapidly quenched alloys of nominal composition Al90Fe7Nb3 and Al94Fe2V4 were studied by Mossbauer spectroscopy. We have measured the recoil‐free fraction and thermal shift at room and liquid nitrogen temperature. The frequency modes of atomic vibrations were determined and consequently the characteristic Debye temperature was derived. Characteristic temperature calculated from f‐factor was lower than those fitted from second order Doppler shift. This indicates the presence of different frequency modes for amorphous and nanocrystalline states.

A constant velocity Mossbauer drive was built with velocity range ±15 mm/s and velocity resolution 0.005 mm/s. Based on good experience with its performance, a new universal CA/CV drive was designed. The new drive is supposed to have velocity range of ±80 mm/s with a velocity resolution below 0.002 mm/s.

The structure, localization of C atoms in the lattice, magnetic moment per Fe atom, coercivity, and the hyperfine interaction parameters of the mechanically alloyed and annealed cementite at 525 and 775 K have been studied using X‐ray diffraction, Mossbauer spectroscopy, and magnetic measurements. The nanocrystalline cementite, (Fe3C)D, with a grain size L⩽10 nm is characterized by carbon atoms occupying both prismatic and octahedral interstices. In the cementite, Fe3C, annealed at 775 K, carbon atoms are localized only in prismatic interstices. Both types of cementite have an orthorhombic lattice (space group Pnma) and close magnetic moments per Fe atom and average hyperfine interaction parameters. The coercivity Hc of the Fe3C is three times higher than that of the (Fe3C)D cementite due to a large magnetocrystalline anisotropy constant.

The NiAs‐type solid solutions based on manganese antimonide Mn1.1Sb with Zn or Cu (up to 10 at % of substituting component) have been studied by 57Fe Mossbauer spectroscopy. It has been shown that the replacement of the manganese antimonide by Cu or Zn does not appreciably affect the main Mossbauer parameters in comparison to those of the parent compound. Two different values of hyperfine magnetic field at Fe are present in all the samples and can be attributed to the metal atoms located in MeI and MeII positions. The substitution of Cu or Zn for manganese antimonide leads to the redistribution of the metal atoms between two cation sublattices.

Hematite was reduced to magnetite and/or wustite on the surfaces of Fe‐Si alloys during annealing in argon in dependence on the annealing temperature and silicon concentration. Hematite film was formed after pre‐annealing in oxygen. Fe‐Si alloys with silicon content of 6, 9, 11 and 14 at.% Si were used in this study. Heat treatments have been performed in vacuum, oxygen and argon atmospheres in the temperature range of 500÷780 °C. Phase analysis has been carried out using Mossbauer spectroscopy and X‐ray diffraction. CEMS measurements showed that the samples which were annealed in vacuum 780 °C have similar Mossbauer parameters like the bulk except that the sextets are shaper due to ordering during heat treatment in vacuum. Samples which were annealed in oxygen showed hematite on their surfaces. The content of hematite on the surfaces of these samples increases by increasing the temperature and decreases by increasing the silicon content. After annealing in argon at 500 and 600 °C, magnetite was formed on...

57Fe Mossbauer spectroscopy in transmission geometry is used for room temperature measurements of the microstructural changes in FINEMET type alloys deformed by in situ tensile stress. The samples in the form of a ribbon are fixed between two jaws of a tensile jig and gradually lengthwise stressed up to the tensile failure. The microstructural changes reflected in the variations of the hyperfine parameters are discussed from the viewpoint of the chemical composition of the amorphous samples, Fe80Nb3Cu1Si6B10 and Fe33.5Ni40Nb3Cu1Si13.5B9. The Mossbauer spectra were analyzed by two Gaussian distributions of hyperfine inductions. Within the mean magnetic induction, also the other hyperfine parameters are evaluated in the particularly deformed states and related to the initial unstressed state of samples. The obtained results indicate the changes in the chemical and topological reordering and the alignment of the magnetic moments in the direction of the applied stress.

Application of Mossbauer spectroscopy with high velocity resolution in biomedical research demonstrated increase of this technique possibility to analyze small variations of the parameters, to study various samples from purified proteins to tissues with high quality measurements and fitting, and to analyze the quality of pharmaceutical compounds.

The physical vapor deposition by cathode arc evaporation (PVD CAE) technique in microdrops mode was applied for deposition of austenitic nanocrystalline coatings of the Fe−31.2%Ni−2%Co−0.002%Y and Fe−31.4%Ni−2%Co−0.72%C−0.001%Y alloys on Cu substrate. The Mossbauer spectroscopy, X‐ray diffraction analysis, transmission electron microscopy and dilatometry have been used to study the structure, magnetic order and thermal expansion of coatings. The estimated coherently diffracting domains values (CDD) and the TEM data testify that austenitic structure in coatings is dispersed and the presence of carbon intensifies the dispersion process of structural elements. Mossbauer analysis has shown that PVD CAE process results in the decomposition of an austenitic solid solution on microareas enriched both in Ni and Co and in Fe, which leads to the formation of a specific magnetic order characterized by existence of the ferromagnetic low‐moment (FM LM) and antiferomagnetic high‐moment (AM HM) phases and provides stabl...

Sensitivity and resolution play a crucial role when Mossbauer spectroscopy is used in the materials science. Application of resonance counters in Mossbauer spectrometers allows us to increase the parameters mentioned above, and also signal‐to‐noise ratio considerably. The last one provides diminishing the time needed for obtaining given statistical accuracy. We carried out investigations of development of optimal counters for following isotopes: 57Fe, 119Sn, and 151Eu. Influence of different parameters of resonant radiation converters on experimental results was considered theoretically. Optimization of design has been performed using mathematical modeling based on Monte‐Carlo method. Comparison of different types of counters used for resonant detecting was carried out. Results of experimental works on selection of efficient radiation converters are given. Comparison of scintillation and gas resonance counters was carried out. FeAl and FeGe2 alloys and K2MgFe(CN)6 have been used as converters for experime...

The effect of a Fe concentration on the dynamics of the phase transitions and on the suppression of the polymorphism in LaMn1−xFexO3+δ(x = 0.015−0.5) has been investigated by Mossbauer spectroscopy and X‐ray diffraction analysis. At a small Fe concentration (x

Study of iron‐bearing phases in ordinary and carbonaceous chondrites as well as iron meteorite and extracted iron‐nickel phosphides by Mossbauer spectroscopy with improved velocity resolution (measurement in 4096 channels, presentation in 1024 channels) demonstrated new results which were not obtained from Mossbauer spectra measured in 512 channels or less. Fitting of the iron meteorite Mossbauer spectrum measured for the first time with presentation in 4096 channels showed new details probably related to the complicated phase composition.

Mossbauer spectroscopy and magnetic measurements were used for an analysis of nanocrystalline iron oxides (hematite α‐Fe2O3, magnetite Fe3O4), Hagg carbide (Fe5C2), and α‐Fe prepared by thermal treatment of synthetic ferrihydrite in various atmospheres. The transformation of ferrihydrite precursor was monitored by the measurements of temperature dependence of magnetic moment (thermomagnetic curves). Under optimized temperature and time, hematite nanoparticles were prepared by heating in vacuum. Application of hydrogen atmosphere yielded magnetite or α‐Fe. Annealing in ethylene resulted in the formation of iron carbides.

Vitreous enameling on steel is carried out to provide a protective layer against chemical corrosion from the surrounding environment. The glass bonds with the steel to form a composite material. The Mossbauer spectroscopy was firstly applied to study the vitreous enameling in which the complex of processes, as diffusion of species, adhesion between the glass and the steel, galvanic reactions, plays an important role. The Mossbauer spectroscopy provides unique information about the Fe‐phase structure of the vitreous enamel layer and that of the steel‐enamel interface. Diffusion of iron from steel surface towards enamel layer and formation of a new Fe2+ phase was proved.

2% of 57Fe doped in Ca1−xSrxRuO3 materials ( x ranging from 0 to 1) were prepared by a sol‐gel method. The influence of the Sr/Ca ratio on the structural and magnetic properties of ruthenates was investigated by XRD and Mossbauer spectroscopy (15 – 300 K). The refined lattice parameters indicate an expansion of the unit cell volume with Sr and a transition of the crystal symmetry from orthorhombic for x < 0.4 to tetragonal for higher Sr content. This transition is also manifested in the 57Fe Mossbauer spectra through the change of: (a) the quadrupole splitting parameter, (∼ 0.1 mm/s for x=0 and ∼0 or slightly negative for x ⩾ 0.4 samples). (b) The isomer shift (c) the magnetic hyperfine parameters (Heff), and (d) the magnetic transition temperature, which increase with x. The temperature dependence of Heff is significantly different for the CaRu0.9857Fe0.02O3 as compared to samples with x = 0.6, 0.8 and 1. In the latter materials, Mossbauer spectra at low temperatures show a much wider distribution in Heff In particular, the field maximum probability decreases progressively with T, whereas for the x=0 material, it remains almost constant. Such behavior is closely related with the literature data on a spin glass ordering of Ca1−xSrxRuO3 with x < 0.2 and a ferromagnetic behavior for the rich Sr samples.

A dynamic study of the thermal decomposition of FeC2O4⋅2H2O has been carried out in air in the range of 25–500 °C with a heating rate of 5 °C/min using the conventional methods of thermal analysis including TG and DSC. The phase composition at different calcination temperatures was determined from 57Fe Mossbauer spectra. It was found that the primary dehydration and liberation of carbon oxides from the oxalate structure is followed by a direct oxidation of Fe(II) to nanocrystalline Fe2O3 with a large surface area of about 250 m2/g. Such nanopowder is comprised of nanocrystalline particles of γ‐ and α‐Fe2O3 as proved by XRD, low temperature Mossbauer spectroscopy and HRTEM analysis. In contradiction with the literature assumption, no traces of magnetite (Fe3O4) have been identified during the oxidative decomposition in air. The simultaneous formation of both γ‐ and α‐Fe2O3 polymorphs at low temperatures is followed by an isochemical structural change of maghemite to hematite. The comparison of Mossbauer spectra taken at different temperatures proves clearly that maghemite appears in samples only as superparamagnetic particles at room temperature (RT), while all sextet components in RT Mossbauer spectra can be assigned to hematite particles with varying size distributions.

Two commercially available modules, a digital oscilloscope (NI 5102) and a function generator (NI 5401) in the PXI (PCI eXtension for Instrumentation) or PCI standard from National Instruments Inc., supported by the driver software, have been used for building a computer‐based Mossbauer spectrometer. The RTSI (Real‐Time System Integration) bus is used for synchronizing the accumulation of the detector impulses to the Mossbauer spectrum with velocity of the “source‐sample” relative motion. The amplitude selection of the impulses from the detector output is based on the use of the Waveform Peak Detection.vi function. This function is available in the graphical programming environment LabVIEW 7 Express which serves for an implementation of the virtual instrument of the Mossbauer spectrometer. Mossbauer spectra can be accumulated in the constant and variable velocity modes; moreover, there is a possibility to register gamma‐ray spectra in the multichannel analyzer mode. Two types of the detectors (a NaI(Tl) and a resonance scintillation detector) have been used with the new Mossbauer spectrometer.