Study of defects in Fe–Re and Fe–Mo alloys by the Mössbauer and positron annihilation spectroscopies

The room temperature positron annihilation lifetime spectra and ⁵⁷Fe Mössbauer spectra were measured for pure Fe as well as for iron-based Fe_1?xRe_x and Fe_1?xMo_x solid solutions with x in the range 0.01≤x≤0.05. The measurements were performed in order to learn more about creation of structural defects during formation and further mechanical processing of the iron systems under consideration. The spectra were collected at least twice for each studied sample synthesized in an arc furnace—after cold rolling to the thickness of about 40 μm as well as after subsequent annealing at 1270 K for 2 h. It was found that in the annealed samples positrons live much shorter than in the not annealed ones which suggest that the latter samples are more defected as it could be expected. Moreover simultaneous analysis of the positron and Mössbauer data shows that cold rolling leads to creation of two types of defects. It seems that they are dislocations and vacancies. Finally from the Mössbauer data it follows that vacancies are located mainly in the vicinity of non-iron atoms, Re or Mo. This speaks in favour of the suggestion that in iron matrix the impurities mentioned above and vacancies interact attractively which supports the known from the literature, theoretical calculations on the Mo-vacancy interaction in iron.     

Evaluation of the detection limit in electron-recording Mössbauer spectroscopy

A semiempirical formula is derived for evaluating the lowest concentration of Mössbauer atoms whose signal can be reliably recorded by electron Mössbauer spectroscopy. The concentration is calculated from the resonance effect magnitude in a sample of known chemical composition, on the basis of the cross sections of photoelectric absorption of source gamma photons by the sample atoms, the energy and probability of production of photoelectrons and their associated Auger electrons, and the probability of recoilless gamma-photon absorption in the sample. Experimental testing showed that the calculated and measured values of differ by not more than 20%.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 20–23, September, 1987.     

Prospects for emission Mössbauer spectroscopy in chemical investigations

Emission Mössbauer spectroscopy is a radiochemical method for investigating materials and the consequences of nuclear transformations taking place in them. Isotopes are traditionally used as structural probes, and the sensitivity of the method is 2–3 orders of magnitude higher than that of absorption Mössbauer spectroscopy. The elements of Mössbauer isotopes with parent nuclei that undergo electron capture or a converted isomeric transition (i.e., lead to high Auger ionization) are the best-studied elements. The electron processes that accompany ionization and their effect on the state of daughter Mössbauer atoms in qualitatively different compounds, from elementary oxides, superconductors, insulators and magnetics to sophisticated bioorganic complexes, are considered.     

Magnetic and Mössbauer studies of fucan-coated magnetite nanoparticles for application on antitumoral activity

Fucan-coated magnetite (Fe₃O₄) nanoparticles were synthesized by the co-precipitation method and studied by Mössbauer spectroscopy and magnetic measurements. The sizes of the nanoparticles were 8–9 nm. Magnetization measurements and Mössbauer spectroscopy at 300 K revealed superparamagnetic behavior. The magnetic moment of the Fe₃O₄ is partly screened by the Fucan coating aggregation. When the magnetite nanoparticles are capped with oleic acid or fucan, reduced particle-particle interaction is observed by Mössbauer and TEM studies. The antitumoral activity of the fucan-coated nanoparticles were tested in Sarcoma 180, showing an effective reduction of the tumor size.     

Broadening of the Mössbauer line for Gaussian spectra

A procedure described byBykov andHien is employed to obtain an approximation formula for the line broadening expected in a Mössbauer experiment for the case where the emission and absorption spectra have Gaussian shapes. For identical emission and absorption spectra, the broadening as given by this formula has an error of less than 4·5% for effective absorber thicknesses up toT _A =10. The case where the emission and absorption spectra have different half widths is also considered.     

Self-tuning digital Mössbauer detection system

Long term gamma spectroscopy experiments involving single-channel analyzer equipment depend upon thermal stability of the detector and its associated high-voltage supply. Assuming constant discrimination levels, a drift in the detector gain impacts the output rate, producing an effect on the output spectrum. In some cases (e.g. single-energy resonant absorption experiments) data of interest can be completely lost. We present a digital self-adapting discrimination strategy that tracks emission line shifts using statistical measurements on a predefined region-of-interest of the spectrum. It is developed in the form of a synthesizable module that can be intercalated in the digital processing chain. It requires a moderate to small amount of digital resources and can be easily activated and deactivated.     

Mössbauer emission spectroscopy of grain boundaries in poly- and nanocrystalline niobium

Grain boundaries in polycrystalline Nb, prepared by cold rolling with subsequent recrystallization annealing, and nanocrystalline Nb, obtained by high-pressure torsion, have been studied by ^119m Sn Mössbauer spectroscopy and the data obtained have been compared.     

Mössbauer antineutrinos: Recoilless resonant emission and absorption of electron antineutrinos

Basic questions concerning phononless resonant capture of monoenergetic electron antineutrinos (Mössbauer antineutrinos) emitted in bound-state β-decay in the ³H-³He system are discussed. It is shown that lattice expansion and contraction after the transformation of the nucleus will drastically reduce the probability of phononless transitions and that various solid-state effects will cause large line broadening. As a possible alternative, the rare-earth system ¹⁶³Ho-¹⁶³Dy is favoured. Mössbauer-antineutrino experiments could be used to gain new and deep insights into several basic problems in neutrino physics.     

Mössbauer emission spectroscopy of pure and doped MgO:57Co

Mössbauer emission studies on ⁵⁷Co embedded in pure and doped MgO have been carried out. The appearance of anomalous ⁵⁷Fe+³ in the Mössbauer spectra is related to the concentration and ionization degree of the electron acceptor levels existing in the energy gap. The temperature dependence of isomer shift of both ferrous and ferric lines agrees well with the Debye model.     

New applications of the Mössbauer effect

Results from a Mössbauer experiment to observe acoustic oscillations induced by pulsed laser excitation in MgO:⁵⁷Fe²⁺ crystal are presented. Time-domain spectra are satsifacorily described by the theory of the frequency modulation of Mössbauer radiation transmitted through a vibrating resonance medium. It is proposed that the D _4Ω/D _2Ω ratio of the fourth and second Fourier harmonics of the modulated radiation be used to measure the amplitude of nuclear oscillations.     

Mössbauer and magnetic characterization of TbRhSn

The intermetallic compound TbRhSn was investigated in detail by X-ray, magnetic susceptibility measurements and ¹¹⁹Sn Mössbauer spectroscopy. This compound undergoes a transition from a paramagnetic to an antiferromagnetic state at T _N = 20.8(2) K. The ¹¹⁹Sn Mössbauer spectrum recorded at 4.2 K can be well fitted as a composition of three subspectra with the same intensities, magnitudes of H _hf, ΔE _Q, and δ _is, in agreement with the model of triangular-like antiferromagnetic arrangements of equal magnetic Tb moments lying in the basal ab-plane deduced from neutron diffraction studies (Szytu?a et al., J Alloys Compd 244:94–98, 1996).     

Mössbauer studies of baotite and bafertisite

The Mössbauer effect was used to study silicate minerals of baotite and bafertisite at 298 K and 95 K. Each spectrum of baotite at 298 K and 95 K consists of two doublets, and they are contributed from Fe²⁺ and Fe³⁺ in the octahedral Tisites, respectively. Each spectrum of bafertisite at 298 K and 95 K is composed of two doublets, and they are mainly caused by Fe²⁺ in the octahedral Fe(I) and Fe(II)sites, respectively. The average effective ionic radii of the Ti sites in baotite and the Fe(I) and Fe(II)sites in bafertisite were estimated based on the correlation of the isomer shifts with the average effective ionic radii in silicates, and they are 0.56 , 0.73 and 0.73 , respectively.     

Mössbauer and X-ray study of the firing process for production of improved roofing tiles

The effects of firing atmosphere parameters on the microstructural characteristics and physical properties of clay roofing tiles were studied. For these investigations, ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry and dilatometry were used. XRD of the raw material exploited from the clay pit belonging to the roofing tile factory “Potisje-Kanjiza”, revealed the presence of montmorillonite, kaolinite, illite and some chlorite clay minerals, as well as, quartz, albite, calcite and dolomite. Gradual changes were observed both in the ⁵⁷Fe Mössbauer spectra and X-ray diffractograms with samples fired in reducing CO/N₂ gas atmosphere at temperatures between 700 and 1060 °C. These changes reflect the dehydroxylation processes, oxide (Fe₃O₄) formation, carbonate decomposition, densification and new silicate (plagioclase) formation. The firing conditions in reducing atmosphere were determined to produce roofing tiles with improved properties.     

Influence of γ-irradiation on properties of amorphous Fe78B13Si9 alloy studied by Mössbauer spectroscopy and positron annihilation technique

The influence of γ-irradiation on properties of METGLAS 2605S2 and FC3-1 Fe₇₈B₁₃Si₉ has been investigated by Mössbauer spectroscopy, positron annihilation technique as well as bending test. The ductility and orientation of magnetization were changed by γ-irradiation. They probably correlate with the change of microscopic free volume and release of stress in the ribbon, respectively.     

Backscattering mirrors for X-rays and Mössbauer radiation

Observation of exact backscattering of X-rays and studies of its energy and angular dependences; test of the validity of the dynamical theory of diffraction in the extreme case of exact backscattering; backscattering high-energy-resolution monochromators; backscattering interferometers, in particular of the Fabry–Pérot interferometer type; and precise, up to 5·10^—9 Å, measurements of crystal lattice parameters: these are central topics of the paper. Special attention is paid to the selection of crystals to be used as backscattering mirrors. Noncubic crystals like Al₂O₃, SiC, etc., allow backscattering for X-rays with practically any energy above 10 keV. Feasibility of backscattering mirrors for Mössbauer radiation of ⁵⁷Fe (14.4 keV), ¹⁵¹Eu (21.5 keV), ¹¹⁹Sn (23.9 keV), and ¹⁶¹Dy (25.6 keV) nuclei is demonstrated by Al₂O₃ crystals. A concrete design of a sapphire Fabry–Pérot–Bragg étalon is presented.

     

Optimization of absorber thickness for the study of Mössbauer spectra of glass

A criterion is proposed for the choice of optimal absorber thickness. The effect of quadrupole splitting, self-absorption, and absorber thickness on the total absorption coefficient and the criterion Q is examined.Translated from Izvestiya Vysshikh Uchebnkh Zavedenii, Fizika, pp. 18–23, No. 1, January, 1986.     

Mössbauer spectroscopy study of interfaces for spintronics

The submonolayer sensitivity and element-specificity of conversion electron Mössbauer spectroscopy, combined with the use of ⁵⁷Fe enriched tracer layers, enable to carefully investigate thin films and interfaces at the atomic-scale. This paper reports on the main achievements we obtained so far in the study of structural, chemical, and magnetic properties of a variety of interfaces between oxides and Fe-based films having potential interest in the field of spintronics.     

Corrosion processes and their inhibition as studied by Mössbauer conversion and other electron spectroscopies

To study corrosion processes of iron and steel and measures of their inhibition, a detailed knowledge of the phase composition and of phase transformations in very thin layers close to the attacked surface of the material is necessary. The information depths of integral (ICEMS) and depth selective (DCEMS) conversion electron Mössbauer spectroscopy are well suited for such investigations, but some effort is necessary if technical samples, i.e. nonenriched in⁵⁷Fe, are to be studied. In many cases of practical importance, full information on the corroded surfaces cannot be got from Mössbauer spectra only, and a combination with Auger and photoelectron spectroscopies, in-including scanning and sputter options, is found to be most informative. This is demonstrated by three examples. The high corrosion resistance of stainless steel X1 CrNiSi 18 15 against boiling HNO₃ is found to be due to a SiO₂ layer formed on the surface and growing with duration of exposure. Nearly no iron oxides are formed, although the composition of the alloy close to the metal surface is slightly influenced. Transformer sheet steel (Fe?3%Si), commercially available after a thermal pretreatment, is covered by an insulating layer containing iron oxides and a large amount of Fe₂SiO₄. By the method combination it was found that a very thick layer below the metallic surface is also modified by the pretreatment. There, one finds pure α-iron containing clusters of SiO₂ which have been formed by internal oxidation. The passivation of iron and steel (DIN 1623) in sulphate solution and in a phosphate buffer was studied in detail. Phase composition and thickness of the passive layer, as thin as a few nm only, were analyzed in dependence on the applied anodic potential and the duration of the passivating procedure. From the experiments, a model of the passive layer was derived, which is a modification of a p-i-n junction proposed elsewhere. The real passivation is ascribed to a layer, only a few monolayers thick, which has a highly disordered structure and provides the transition from cubic to orthorhombic structure. Some thermodynamical considerations show that immediately on an iron substrate, an oxide layer should always contain a high concentration of Fe²⁺ forming an equilibrium oxide. The absence of Fe²⁺ in Mössbauer spectra is interpreted by the assumption that this layer may be extremely thin, i.e. a few monolayers only.     

Comparative Mössbauer study of the aging of Fe-C and Fe-N martensites

The clustering-ordering synergy which forms Fe₆C precipitates by aging Fe-C martensite is compared to the long-range ordering which forms Fe₁₆N₂ by aging Fe-N martensite.