Analysis of the iron states in iron-containing pharmaceutical products using Mössbauer spectroscopy

Iron-containing pharmaceuticals, namely: (i) PreNatal with ferrous fumarate, (ii) Tardyferon® with ferrous sulfate, (iii) Fenules with water free ferrous sulfate, (iv) Iron Complex with iron glycinate, citrate, (v) Gentle Iron, (vi) Hema-Plex® and (vii) Iron Bisglycinate with iron (ferrous) bisglycinate chelate (iron compounds are given as declared by the manufactures) were studied by 57Fe Mössbauer spectroscopy with X-ray diffraction and magnetization measurements for analysis of the iron state. The obtained results demonstrate that the iron compound announced by the manufacturer in each pharmaceutical is not homogeneous and exists as some modifications of this compound or results of its transformation/oxidation probably due to its instability. The presence of ferrous and ferric compounds is observed, and the relative ferric iron fractions are roughly determined for each pharmaceutical product. This analysis clearly shows the differences between the iron compounds proclaimed by the manufacturers and those obtained by Mössbauer spectroscopy. That justifies as to why this technique should be used for the control and analysis of the iron-containing pharmaceuticals.

Luminescence in Anion-Deficient Hafnia Nanotubes

Hafnia-based nanostructures and other high-k dielectrics are promising wide-gap materials for developing new opto- and nanoelectronic devices. They possess a unique combination of physical and chemical properties, such as insensitivity to electrical and optical degradation, radiation damage stability, a high specific surface area, and an increased concentration of the appropriate active electron-hole centers. The present paper aims to investigate the structural, optical, and luminescent properties of anodized non-stoichiometric HfO2 nanotubes. As-grown amorphous hafnia nanotubes and nanotubes annealed at 700 °C with a monoclinic crystal lattice served as samples. It has been shown that the bandgap Eg for direct allowed transitions amounts to 5.65 ± 0.05 eV for amorphous and 5.51 ± 0.05 eV for monoclinic nanotubes. For the first time, we have studied the features of intrinsic cathodoluminescence and photoluminescence in the obtained nanotubular HfO2 structures with an atomic deficiency in the anion sublattice at temperatures of 10 and 300 K. A broad emission band with a maximum of 2.3-2.4 eV has been revealed. We have also conducted an analysis of the kinetic dependencies of the observed photoluminescence for synthesized HfO2 samples in the millisecond range at room temperature. It showed that there are several types of optically active capture and emission centers based on vacancy states in the O3f and O4f positions with different coordination numbers and a varied number of localized charge carriers (V0, V-, and V2-). The uncovered regularities can be used to optimize the functional characteristics of developed-surface luminescent media based on nanotubular and nanoporous modifications of hafnia.

Computational prediction of new magnetic materials

The discovery of new magnetic materials is a big challenge in the field of modern materials science. We report the development of a new extension of the evolutionary algorithm USPEX, enabling the search for half-metals (materials that are metallic only in one spin channel) and hard magnetic materials. First, we enabled the simultaneous optimization of stoichiometries, crystal structures, and magnetic structures of stable phases. Second, we developed a new fitness function for half-metallic materials that can be used for predicting half-metals through an evolutionary algorithm. We used this extended technique to predict new, potentially hard magnets and rediscover known half-metals. In total, we report five promising hard magnets with high energy product (|BH|_MAX), anisotropy field (H_a), and magnetic hardness (κ) and a few half-metal phases in the Cr-O system. A comparison of our predictions with experimental results, including the synthesis of a newly predicted antiferromagnetic material (WMnB₂), shows the robustness of our technique.

Impact of oxygen content on preferred localization of p- and n-type carriers in La0.5Sr0.5Fe1-xMnxO3-δ

The oxygen content in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ, measured by coulometric titration in a wide range of oxygen partial pressure at various temperatures, was used for defect chemistry analysis. The obtained data were well approximated by a model assuming defect formation in La_0.5Sr_0.5Fe_1-xMn_xO_3-δvia Fe³⁺ and Mn³⁺ oxidation reactions and charge disproportionation on Fe³⁺ and Mn³⁺ ions. The partial molar enthalpy and entropy of oxygen in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ obtained by statistical thermodynamic calculations were found to be in satisfactory agreement with those obtained using the Gibbs-Helmholtz equations, thus further confirming the adequacy of the model. The impact of manganese substitution on defect equilibrium in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ was shown to be attributed to a lower enthalpy of Mn³⁺ oxidation reaction (vs. for the oxidation of Fe³⁺) and the charge disproportionation reaction on Mn³⁺ (vs. for that on Fe³⁺). The former makes Mn⁴⁺ ions more resistant to reduction than Fe⁴⁺. The latter favors the presence of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in oxides in comparable concentrations. The distribution of charge carriers over iron and manganese ions was determined as a function of oxygen content in La_0.5Sr_0.5Fe_1-xMn_xO_3-δ.

Bjurböle L/LL4 ordinary chondrite properties studied by Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

Bjurböle L/LL4 ordinary chondrite was studied using scanning electron microscopy with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy. The phase composition and the relative iron fractions in the iron-bearing phases were determined. The unit cell parameters for olivine, orthopyroxene and clinopyroxene are similar to those observed in the other ordinary chondrites. The higher contents of forsterite and enstatite were detected by Raman spectroscopy. Magnetization measurements showed that the temperature of the ferrimagnetic-paramagnetic phase transition in chromite is around 57 K and the saturation magnetic moment is ~7 emu/g. The values of the ⁵⁷Fe hyperfine parameters for all components in the Bjurböle Mössbauer spectrum were determined and related to the corresponding iron-bearing phases. The relative iron fractions in Bjurböle and the ⁵⁷Fe hyperfine parameters of olivine, orthopyroxene and troilite were compared with the data obtained for the selected L and LL ordinary chondrites. The Fe²⁺ occupancies of the M1 and M2 sites in silicate crystals were determined using both X-ray diffraction and Mössbauer spectroscopy. Then, the temperatures of equilibrium cation distribution were determined, using two independent techniques, for olivine as 666 K and 850 K, respectively, and for orthopyroxene as 958 K and 1136 K, respectively. Implications of X-ray diffraction, magnetization measurements and Mössbauer spectroscopy data for the classification of the studied Bjurböle material indicate its composition being close to the LL group of ordinary chondrites.

Characterization of Kemer L4 meteorite using Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

The bulk interior of Kemer L4 ordinary chondrite was characterized for the first time by means of optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy with a high velocity resolution. The main and minor iron-bearing phases were found as well as ferrihydrite as a result of weathering. The Fe²⁺ partitioning among the M1 and M2 sites in olivine, orthopyroxene and clinopyroxene was determined from the X-ray diffraction. The ratios of Fe²⁺ occupancies for these crystals were estimated from both X-ray diffraction and Mössbauer spectroscopy data and appeared to be in a good agreement. The distribution coefficients K_D and the temperatures of equilibrium cation distribution T_eq were also evaluated for olivine and orthopyroxene from two independent techniques and were in a good consistence: K_D = 1.77, T_eq = 441 K (X-ray diffraction) and K_D = 1.77, T_eq = 439 K (Mössbauer spectroscopy) for olivine and K_D = 0.10, T_eq = 806 K (X-ray diffraction) and K_D = 0.09, T_eq = 787 K (Mössbauer spectroscopy) for orthopyroxene. The fusion crust of Kemer L4 was studied using X-ray diffraction, magnetization measurements and Mössbauer spectroscopy. Magnesioferrite and probably maghemite were found in the fusion crust in addition to other phases observed in the bulk interior.

The interior and the fusion crust in Sariçiçek howardite: Study using X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

The meteorite Sariçiçek, a 2015 howardite fall in Turkey, was analyzed using various physical techniques. Both the interior and the fusion crust were studied by optical and scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, magnetization measurements and Mössbauer spectroscopy. The main and minor iron-bearing phases such as orthopyroxene, Ca-poor and Ca-rich clinopyroxene, chromite with hercynite, Fe²⁺ and Fe³⁺ ilmenite, troilite, α-Fe(Ni, Co), α₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases were identified. The ratios of Fe²⁺ occupancies in the M1 and M2 sites in the silicate phases as well as the equilibrium Fe²⁺ and Mg²⁺ cations distribution temperatures (T_eq) for orthopyroxene were estimated using X-ray diffraction and Mössbauer spectroscopy, which appeared to be in a good agreement: for example, T_eq were 886 and 878 K, respectively. The glass-like fusion crust of Sariçiçek consists of orthopyroxene with ferrous and ferric compounds that are likely products of combustion and melting.

Variability of Chelyabinsk meteoroid stones studied by Mössbauer spectroscopy and X-ray diffraction

The meter-scale variations of material properties of the 20-m sized Chelyabinsk meteoroid are critical for understanding why the meteoroid fragmented the way it did and caused the devastating airburst that sent over 1600 people to the hospital for treatment of glass cuts and minor injuries on February 15, 2013. From a range of differently looking unweathered meteorite fragments that were recovered shortly after the event, these material differences were probed by means of optical and scanning electron microscopy, X-ray diffraction (XRD), and the high velocity resolution Mössbauer spectroscopy. All main and some minor iron-bearing phases were identified on the basis of XRD data and Mössbauer spectra. The Fe²⁺ partitioning between the M1 and M2 sites in silicate phases was determined independently using XRD and Mössbauer data. Different meteorite fragments show a range of 570-1180 K in the temperature of the Fe²⁺ and Mg²⁺ equilibrium distribution between the M1 and M2 sites in olivine, while that in orthopyroxene falls in the range 870-1180 K (these ranges were estimated using both techniques). This fact points out a slightly different thermal history of these minerals before they accumulated in different parts of the Chelyabinsk meteoroid. The Chelyabinsk meteoroid is a fragmental breccia from materials formed at different depths in their parent body, or from materials that experienced different annealing temperatures in impacts. In addition, the fusion crust from two fragments, studied by XRD and Mössbauer spectroscopy, experienced a different thermal history during entry, suggesting that the fragment with mixed light and dark lithologies was located deeper inside the initial meteoroid than the fragment with only light lithology, or fragmented less readily.

Characterization of Northwest Africa 6286 and 7857 ordinary chondrites using X-ray diffraction, magnetization measurements and Mössbauer spectroscopy

Northwest Africa (NWA) 6286 and 7857 meteorites were studied in detail by using optical microscopy, scanning electron microscopy with energy dispersion spectroscopy, X-ray diffraction, magnetization measurements and ⁵⁷Fe Mössbauer spectroscopy with a high velocity resolution. The main and the minor iron-bearing phases were identified in both meteorites. The unit cell parameters as well as Fe²⁺ and Mg²⁺ cation distribution were determined for the M1 and M2 sites in silicate microcrystals. Saturation magnetic moments were obtained for both meteorites. Mössbauer parameters for the main and the minor iron-bearing microcrystals were estimated and compared for NWA 6286 and NWA 7857 LL6 ordinary chondrites. The Fe²⁺ and Mg²⁺ cation partitioning, distribution coefficient and temperature of cation equilibrium distribution were estimated for silicate microcrystals using X-ray diffraction and Mössbauer spectroscopy.

Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations

The structures of several fluoroscandate compounds are presented here using a characterization approach combining powder X-ray diffraction and solid-state NMR. The structure of K₅Sc₃F₁₄ was fully determined from Rietveld refinement performed on powder X-ray diffraction data. Moreover, the local structures of NaScF₄, Li₃ScF₆, KSc₂F₇, and Na₃ScF₆ compounds were studied in detail from solid-state ¹⁹F and ⁴⁵Sc NMR experiments. The ⁴⁵Sc chemical shift ranges for six- and seven-coordinated scandium environments were defined. The ¹⁹F chemical shift ranges for bridging and terminal fluorine atoms were also determined. First-principles calculations of the ¹⁹F and ⁴⁵Sc NMR parameters were carried out using plane-wave basis sets and periodic boundary conditions (CASTEP), and the results were compared with the experimental data. A good agreement between the calculated shielding constants and experimental chemical shifts was obtained. This demonstrates the good potential of computational methods in spectroscopic assignments of solid-state ⁴⁵Sc NMR spectroscopy.

57Fe Mössbauer spectroscopy and electron paramagnetic resonance studies of human liver ferritin, Ferrum Lek and Maltofer®

A human liver ferritin, commercial Ferrum Lek and Maltofer® samples were studied using Mössbauer spectroscopy and electron paramagnetic resonance. Two Mössbauer spectrometers have been used: (i) a high velocity resolution (4096 channels) at 90 and 295K, (ii) and a low velocity resolution (250 channels) at 20 and 40 K. It is shown that the three studied materials have different superparamagnetic features at various temperatures. This may be caused by different magnetic anisotropy energy barriers, sizes (volume), structures and compositions of the iron cores. The electron paramagnetic resonance spectra of the ferritin, Ferrum Lek and Maltofer® were decomposed into multiple spectral components demonstrating the presence of minor ferro- or ferrimagnetic phases along with revealing marked differences among the studied substances. Mössbauer spectroscopy provides evidences on several components in the measured spectra which could be related to different regions, layers, nanocrystallites, etc. in the iron cores that coincides with heterogeneous and multiphase models for the ferritin iron cores.