Adriana Lančok

Iron is one of the most abundant elements on Earth and also in Mössbauer research. The present study is a summary of our search for iron compounds that now play an important role in the development of specific areas of inorganic chemistry of iron, biological applications and pigment for various types of artworks. The different catalytic or biologically active systems were studied in particular of the Mössbauer spectrometry, including temperature dependencies of the biological tissue and the synthetic vivianite. Mössbauer spectrometry was chosen as the main investigation tool for identification of Fe²⁺ and Fe³⁺. We are identified divalent and trivalent iron in the samples and we found their mutual ratio. The iron sandwich complexes exhibit a linear dependence between quadrupole splitting and number of methyl groups. We also determined temperature of transformation of divalent to trivalent iron for vivianite sample that are used in painting. The transformation temperature is about 90°C.

The long-term reliability of construction materials operating in nuclear facilities under harsh conditions such as intense irradiation, high temperature, and in the presence of corrosion agents is a serious technologic, economic, and environmental demand. In this work, we elucidate the structural features of advanced corrosion-resistant LC 200N steel. High Cr and N contents provide high hardness and wear resistance of this perspective material which can be considered for possible applications in nuclear installations. Structural arrangement was checked by scanning electron microscopy and transmission electron microscopy. Chemical composition was inspected by X-ray fluorescence technique, spark optical emission spectroscopy, and neutron activation analysis. Mössbauer spectrometry was chosen as the principal method of investigation. Conversion Electron Mössbauer Spectrometry and transmission techniques were applied.

We studied the effect of interfaces character in 57Fe/Au thin layers on iron hyperfine parameters using Mössbauer spectroscopy. Four samples of bilayers (57Fe covered by Au) were prepared on MgO substrate by pulsed laser deposition (PLD) with varying 57Fe layer thickness (∼10–95 nm), covered by Au layer with constant thickness of ∼8.7 nm. Mössbauer spectra were acquired in transmission and conversion electron geometry. The hyperfine parameters of α–Fe layer, Fe/Au and MgO/Fe interfaces were determined.

Iron is an essential element for fundamental cell functions and a catalyst for chemical reactions. Three samples extracted from the human spleen were investigated by scanning (SEM) and transmission electron microscopy (TEM), Mössbauer spectrometry (MS), and SQUID magnetometry. The sample with diagnosis of hemosiderosis (H) differs from that referring to hereditary spherocytosis and the reference sample. SEM reveals iron-rich micrometer-sized aggregate of various structures—tiny fibrils in hereditary spherocytosis sample and no fibrils in hemochromatosis. Hematite and magnetite particles from 2 to 6 μm in TEM with diffraction in all samples were shown. The SQUID magnetometry shows different amount of diamagnetic, paramagnetic and ferrimagnetic structures in the tissues. The MS results indicate contribution of ferromagnetically split sextets for all investigated samples. Their occurrence indicates that at least part of the sample is magnetically ordered below the critical temperature. The iron accumulation process is different in hereditary spherocytosis and hemosiderosis. This fact may be the reason of different iron crystallization.

Low temperature (4.2 K) magnetic behavior of Fe₇₆Mo₈Cu₁B₁₅ metallic glass was studied by ⁵⁷Fe Mössbauer spectrometry (MS) and ⁵⁷Fe NMR. Distributions of hyperfine magnetic fields P(B) were determined for as-quenched and annealed (nanocrystalline) samples with relative fraction of the grains about 43%. P(B) distributions were derived for both the amorphous matrix and nanocrystalline grains. NMR of alloys with natural and ⁵⁷Fe enriched Fe enabled to assess the contribution of ¹¹B to the total NMR signal. P(B) distribution of the as-quenched alloy derived from MS matches reasonably well the one from NMR of the enriched sample. NMR signal from the sample with natural Fe exhibits contributions from ¹¹B nuclei. The principal NMR lines of the annealed alloys at 47 MHz correspond to bcc Fe nanocrystals. Small asymmetry of the lines towards higher frequencies might be an indication of possible impurity atoms in the bcc structure. The observed differences between natural and enriched samples are attributed to higher sensitivity in the latter. Positions of the lines attributed to bcc Fe nanocrystals obtained from MS and NMR are in perfect agreement.

The nanoparticles of ε-Fe₂O₃ enriched with ⁵⁷Fe isotope in amorphous silica matrix were prepared by sol-gel technique starting from a single molecular precursor for both Fe₂O₃ and silica. From the X-ray powder diffraction pattern ε-Fe₂O₃ was identified as the major phase and α-Fe₂O₃ and β-Fe₂O₃ were observed as minor iron oxide phases. Using the log-normal distribution for fitting the experimental data from the TEM micrographs, the characteristic size of particles d₀ ∼ 25 nm was derived. The rather high coercivity of ∼2.1 T at room temperature was confirmed for our nanoparticle system. From the dependences of magnetization on temperature a two-step magnetic transition spread between 100 K and 153 K was indicated. From the ⁵⁷Fe Mössbauer spectra measured in the temperature range of 4.2–300 K, the hyperfine parameters for one tetrahedral and three octahedral sites of ε-Fe₂O₃ structure were identified. The in-field spectra in the external magnetic fields up to 6 T were taken both above and below the indicated two-step magnetic transition. Their dependence on temperature and external magnetic field suggests that the first step in the temperature range of 153 K–130 K is related to the spin reorientation of the local magnetic moments in the magnetic sublattices and the second step in temperatures 130 K–100 K may be associated with the intermediate spin–high spin state transition of Fe³⁺ cation in the tetrahedral sublattice expressed in the change of the hyperfine magnetic field.