Mössbauer spectroscopy on57Fe: NaCl crystals

Mössbauer absorbtion spectra of⁵⁷Fe-doped NaCl crystal were measured and correlated with an adequate electric field gradient computation to describe the dipolar complexes occuring at the decay of Suzuki-phase under thermal treatment and X-ray irradiation. An electrostatic potential of the type was taken into account in the evaluation of EFG tensor.     

Mössbauer spectroscopy in catalysis

Application of in situ Mössbauer spectroscopy for studying catalysts and catalytic processes is discussed. Examples are presented to illustrate the potentials of the method by describing studies on supported heterogeneous catalysts performed with ¹¹⁹Sn and ⁵⁷Fe spectroscopies in cases with certain metals and alloys, oxides and porous substances. The results are interpreted in comparison to the catalytic performance.     

Chemical states of localized Fe atoms in ethylene matrices using in-beam Mössbauer spectroscopy

The reaction products of isolated single iron atoms in a low concentration matrix of ethylene were studied using in-beam Mössbauer spectroscopy with a short-lived ⁵⁷Mn (T _1/2=1.45 m) beam. The in-beam Mössbauer spectrum of ⁵⁷Fe arising from ⁵⁷Mn in a matrix of ethylene and argon measured at 16 K was analyzed with four components. Density functional theory calculations were carried out to confirm the assignments. It was suggested that the reaction produced monoiron species of Fe(C ₂ H ₄) with a spin state of S = 2.     

Mössbauer spectroscopy with actinide elements

Although formally equivalent to the lanthanide (4f) elements, the light actinides show a much more varied behaviour due to the larger spatial extent and ionizability of the 5f electrons. The application of Mössbauer spectroscopy for the determination of electronic properties of the actinides is outlined. Emphasis is put on high pressure Mössbauer experiments using the 60 keV transition in²³⁷Np to study questions of delocalization of 5f electrons.Work performed under the auspices of the Bundesministerium für Forschung und Technologie, Federal Republic of Germany.     

Fe/Dy artificial multilayered films studied by57Fe Mössbauer spectroscopy

Magnetic properties of multilayered Fe/Dy films with artificial superstructures have been investigated by⁵⁷Fe Mössbauer spectroscopy. Doublet peaks are observed at room temperature when the Fe layer is thinner than 20Å. Mössbauer spectra for thicker Fe layers correspond to α-Fe spectra. In certain samples, i.e. [Fe(44Å)/Dy(6Å)], a gradual spin reorientation takes place, which is evidenced from the change of relative intensities of Δm=0 lines with decreasing temperature.     

Mössbauer NMR double resonance in57Fe. Coupling between quadrupole split states

In order to describe the interaction of a nucleus (in a static electric field gradient) with a radiation field, we have introduced the concept of dressed nucleus. The eigenvalues of its Hamiltonian are calculated, which leads to expressions for the different energies of -rays produced by spontaneous emission. We have calculated these energies as well as their relative probabilities in the case ofI _e=3/2^--I_g=1/2^- Ml transitions. We have shown that a Mössbauer spectrum using as a source an ensemble of dressed nuclei and a single line absorber consists of six lines: two lines of the original quadrupole doublet and four sidebands, each of them having the same intensity.     

Atomic short-range order in Fe1−xCrx alloys studied by 57Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for iron-based solid solutions Fe_1?xCr_x with x in the range of 0.01≤x≤0.10. Analysis of the obtained spectra gave clear evidence that the distribution of impurity atoms in the first coordination spheres of ⁵⁷Fe nuclei is not homogeneous and it cannot be described in terms of binomial distribution. Quantitatively, the effects were described in terms of the short-range order parameters.     

Fe57 Mössbauer study in cobalt substituted magnetite

The Mössbauer effect has been studied in the mixed ferrites Co _x Fe_3–x O₄ (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe³⁺ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe³⁺ and Fe²⁺, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe³⁺ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed.     

Mössbauer spectroscopy in physical metallurgy

In this anniversary contribution the natural and intimate match making which occurs between the two star performers-⁵⁷Fe in Mössbauer spectroscopy and iron in physical metallurgy—is described by selecting typical examples reflecting the author's interest: phases, f.c.c. -Fe, defects, diffusion and amorphous metals.     

Mössbauer spectroscopy in molecular magnetism

The aim of this paper is to highlight some selected research activities on molecular magnetic materials using Mössbauer spectroscopy as a technique carried out in our laboratory in recent years. The first part of the present article is devoted to the studies of the various magnetic interactions, metal-to-metal electron-transfer phenomenon, glass transition occurring in molecular magnetic materials, whereas the second part deals with the iron(II) high spin (S = 2)–low spin (S = 0) transition phenomenon occurring in some isoxazole ligand based iron(II) compounds as examples with unusually complicated spin transition behaviour. Also, an example of a dinuclear a spin crossover compound of iron(II) is described, where Mössbauer spectroscopy has most convincingly unraveled the mechanism of the spin transition process. Finally, an example from our most recent studies of spin crossover materials exhibiting both thermal spin crossover and liquid crystalline properties in the same temperature interval near room temperature will be presented.     

Mössbauer spectroscopy of the Zr-rich region in Zr–Nb–Fe alloys with low Nb content

Intermetallic phases and solid solutions in the Zr-rich region of the Zr–Nb–Fe system with low Nb content are studied by Mössbauer spectroscopy complemented with X-ray diffraction, optical and scanning electron microscopy and electron microprobe analysis. The phases found in each sample were those expected from the corresponding binary Zr–Fe system. Furthermore, one of the samples showed a ternary cubic Ti₂Ni type phase with a similar stoichiometry to the tetragonal Zr₂Fe compound. Mössbauer parameters were suggested to this phase (IS: - 0.12 mm/s, QS: 0.30 mm/s), to the bcc Zr(β) phase (IS: (-0.11 α 0.01) mm/s, QS: (0.23 α 0.02) mm/s), and to the hcp Zr(β^T) phase (IS: (-0.24 α 0.02) mm/s, QS: (0.45 α 0.02) mm/s).     

Characterization of T-55 sorbent using 57Fe Mössbauer spectroscopy with a high velocity resolution

A new sorbent T-55 with mixed ferrocyanide surface modification developed for Cs⁺ sorption was characterized using Mössbauer spectroscopy with a high velocity resolution in comparison with K₂Ni[Fe(CN)₆] and K₄[Fe(CN)₆ samples. The main sorption active component of T-55 sorbent was determined as K₂Ni[Fe(CN)₆].     

Mössbauer spectroscopy with the 93 keV-resonance in67Zn

The procedures and results of high resolution Mössbauer experiments performed with the 93.3 keV resonance in absorbers of⁶⁷ZnO,⁶⁷ZnS (both wurtzite and sphalerite structures),⁶⁷ZnSe,⁶⁷ZnTe and⁶⁷ZnF₂ are reported. An essentially linear dependence between the isomer shift and the Pauling electronegativity of the ligands was found. A value of r ²=+11×10^–3 fm² is estimated. The Mössbauer parameters for both ZnS structures are equal within present limits of error. In particular, no quadrupole interaction was observed in the wurtzite modification. This indicates a nearly identical local symmetry at the Zn site in the two ZnS structures.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany and the Kernfor-schungszentrum Karlsruhe     

Mössbauer spectroscopy of Al substituted Fe in holmium iron garnet

A Mössbauer spectroscopy study was made on Ho₃Fe_5-xAl_xO₁₂ (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (B_hf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with B_hf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in B_hf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.     

A 57Fe Mössbauer spectroscopy study of iron nanoparticles obtained in situ in conversion ferrite electrodes

Transmission Mössbauer spectroscopy and CEMS are powerful tools to study the changes in which iron-containing active materials of conversion electrodes are involved during lithium cell charge and discharge. The usual spectrum of pristine CoFe₂O₄ spinel with two sextets ascribable to Fe^3?+? ions in both tetrahedral and octahedral environments, changes dramatically after cell discharge to 0 V vs. Li, and can be interpreted as the result of iron reduction to the metallic state in the form of superparamagnetic metal nanoparticles dispersed in a Li₂O matrix. After cell charge to 3 V, the MS of the pristine sample is not recovered. Instead, two new doublets are visible with IS ascribable to Fe^3?+? ions. ⁵⁷Fe CEMS evidences the different environment of iron atoms in the surface of the nanodispersed material found in the used electrodes.     

Mössbauer effect diffraction from polycrystalline57Fe

We built a Debye-Scherrer type powder diffractometer with a⁵⁷Co radiation source and a large-angle position-sensitive detector. We tuned the incident -ray beam on and off the Mössbauer effect resonance, and measured diffraction patterns from our textured samples of polycrystalline⁵⁷Fe. Mössbauer effect diffraction dominated over X-ray diffraction for the higher order Bragg peaks.     

Digital pulse processing in Mössbauer spectroscopy

In this work we present some advances towards full digitization of the detection subsystem of a Mössbauer transmission spectrometer. We show how, using adequate instrumentation, preamplifier output of a proportional counter can be digitized with no deterioration in spectrum quality, avoiding the need of a shaping amplifier. A pipelined architecture is proposed for a digital processor, which constitutes a versatile platform for the development of pulse processing techniques. Requirements for minimization of the analog processing are considered and experimental results are presented.     

Synchrotron Mössbauer source of57Fe radiation

A nonradioactive source of Mössbauer radiation is described for use in Mössbauer absorption and scattering spectroscopy. The radiation is generated by synchrotron Xrays in an iron borate single crystal set in diffraction conditions at the Néel temperature (75.3°C). Like a conventional Mössbauer source the new Synchrotron Mössbauer (SM) source emits singleline radiation of about natural linewidth, but in addition the emitted radiation is fully recoilless, highly directed and of pure linear polarization. An extremely high suppression of the electronic scattering is achieved. The latter circumstance allows one to perform Mössbauer experiments using pulsed synchrotron radiation in a steady state mode as in a normal Mössbauer measurement.The theory of the SM source is developed. First Mössbauer spectra obtained with the SM source are shown. Applications of the SM source are discussed.     

57Fe quadrupole splitting and isomer shift in various oxyhemoglobins: study using Mössbauer spectroscopy

A comparative study of normal human, rabbit and pig oxyhemoglobins and oxyhemoglobin from patients with chronic myeloleukemia and multiple myeloma using Mössbauer spectroscopy with a high velocity resolution demonstrated small variations of the ⁵⁷Fe quadrupole splitting and isomer shift. These variations may be a result of small structural differences in the heme iron stereochemistry of various hemoglobins.