Search Results (84)

This work investigated the electrical, dielectric, and magnetic properties of ferrofluids containing Fe₃O₄ nanoparticles and their composites with chitosan (30–100 cP and 100–300 cP), relevant to magnetic hyperthermia. The nanoparticles were synthesized by coprecipitation and characterized using impedance spectroscopy, X-ray diffraction, scanning microscopy with X-ray microanalysis, Mössbauer spectroscopy, and calorimetry. The study showed that the chitosan coating altered the textural properties of Fe₃O₄, reducing the specific surface area from 76.3 m²/g to 68.9–72.5 m²/g. The zeta potential and particle size showed strong pH dependence. Impedance measurements showed that the conductivity of ferrofluids was frequency- and temperature-dependent, with both metallic and dielectric conductivity observed. The complex dielectric permittivity exhibited Maxwell–Wagner–Sillars interface polarization. Calorimetry revealed that specific absorption rate (SAR) ranged from 11.4 to 23.4 W/g, depending on the chitosan concentration and type, while the chitosan coating reduced SAR by 12–40%. These results confirm that the electrical and dielectric parameters of ferrofluids significantly influence their thermal capabilities, which is important for optimizing magnetic hyperthermia therapy when energy dissipation is considered in bio-heat models. Full article

This article introduces the main characteristics of PyMossFit, a software for Mössbauer spectra fitting. It is explained how each aspect of the code works. Based on the Lmfit Python package, it is a robust data fitting tool. Designed to run through Jupyter Notebook in the Google Colab cloud, it also allows one to work via multiple devices and operating systems. In addition, it allows the fitting procedure to be performed collaboratively among researchers. The software performs the folding of raw data with a discrete Fourier transform. Data smoothing is available with the use of a Savitzky–Golay algorithm. Moreover, a K-nearest neighbor algorithm enables users to determine the present phases by matching the correlations of hyperfine parameters from a local database. Full article

Hematite nanoparticles ($\mathrm{\alpha }-{\mathrm{Fe}}_2{\mathrm{O}}_3 \mathrm{NPs}$) were synthesized through a thermal conversion of synthetic and biosynthesized nanomaghemite ($\mathrm{\gamma }-{\mathrm{Fe}}_2{\mathrm{O}}_3 \mathrm{NPs}$) precursors. X-ray diffraction data confirmed phase-pure hematite with crystallite sizes of 54 and 56 nm for the H1 and H2 samples, respectively. Transmission electron microscopy (TEM) revealed a bimodal-like distribution feature (peaks at 18.5 and 35.5 nm) for the H1 sample, while the histogram plot of the H2 sample displayed a homogeneous particle size distribution with a mean size of 28 nm. X-ray photoelectron spectroscopy confirmed Fe³⁺ ions as the dominant oxidation state in both samples. In addition, while ⁵⁷Mössbauer spectroscopy indicated relaxation effects and line broadening for the H1 sample at both 300 K and 16 K, consistent with incomplete $\mathrm{\gamma }\to \mathrm{\alpha }$ transformation, the H2 sample exhibited spectra at the same temperatures resembling a bulk-like hematite. Magnetometry supported these findings since the H1 sample showed enhanced coercivity (2.2 kOe) and remanence (0.23 emu/g), features attributed to a residual ferrimagnetic contribution of $\mathrm{\gamma }-{\mathrm{Fe}}_2{\mathrm{O}}_3 \mathrm{NPs}$, and the H2 sample exhibited weaker ferromagnetism, as typically found in nanoscale hematite. These results highlight the synergistic use of X-ray photoelectron and Mössbauer spectroscopies, and magnetic measurements to reveal subtle multiphase coexistence, demonstrating that precursor chemistry and biosynthetic functionalization decisively govern the structural and magnetic evolution of $\mathrm{\gamma }\to \mathrm{\alpha }-{\mathrm{Fe}}_2{\mathrm{O}}_3 \mathrm{NPs}$. Full article

The vibration properties of materials play a role in their conduction of electric charges. Ionic conductors such as electrodes and solid electrolytes are also relevant in this respect. The vibration properties are typically assessed with infrared and Raman spectroscopy, and inelastic neutron scattering, which all allow for the derivation of the phonon density of states (PDOS) in part of a full portion of the Brioullin zone. Nuclear resonant vibration spectroscopy (NRVS) is a novel method that produces the element-specific PDOS from Mössbauer-active isotopes in a compound. We employed NRVS operando on a pouch cell battery containing a Li⁵⁷FePO₄ electrode, and thus could derive the PDOS of the ⁵⁷Fe in the electrode during charging and discharging. The spectra reveal reversible vibrational changes associated with the two-phase conversion between LiFePO₄ and FePO₄, as well as signatures of metastable intermediate states. We demonstrate how the NRVS data can be used to tune the atomistic simulations to accurately reconstruct the full vibration structures of the battery materials in operando conditions. Unlike optical techniques, NRVS provides bulk-sensitive, element-specific access to the full phonon spectrum under realistic operando conditions. These results establish NRVS as a powerful method to probe lattice dynamics in working batteries and to advance the understanding of ion transport and phase transformation mechanisms in electrode materials. Full article

In the present work, we describe the use of the potentially tridentate ligand pyridine-2-amidoxime (NH₂paoH) in Fe-Co chemistry. The 1:1:3 Fe^III(NO₃)₃·9H₂O/Co^II(ClO₄)₂·6H₂O/NH₂paoH reaction mixture in MeOH gave complex [Co^III₂Fe^III(NH₂pao)₆](ClO₄)₂(NO₃) (1) in ca. 55% yield, the cobalt(II) being oxidized to cobalt(III) under the aerobic conditions. The same complex was isolated using cobalt(II) and iron(II) sources, the oxidation now taking place at both metal sites. The structure of 1 contains two structurally similar, crystallographically independent cations [Co^III₂Fe^III(NH₂pao)₆]³⁺ which are strictly linear by symmetry. The central high-spin Fe^III ion is connected to each of the terminal low-spin Co^III ions through the oximato groups of three 2.1110 (Harris notation) NH₂pao⁻ ligands, in such a way that the six O atoms are bonded to the octahedral Fe^III center ({Fe^IIIO₆} coordination sphere). Each terminal octahedral Co^III ions is bonded to six N atoms (three oximato, three 2-pyridyl) from three NH₂pao⁻ groups ({Co^IIIN₆} coordination sphere). The IR and Raman spectra of the complex are discussed in terms of the coordination mode of the organic ligand, and the non-coordinating nature of the inorganic ClO₄⁻ and NO₃⁻ counterions. The UV/VIS spectrum of the complex in EtOH shows the two spin-allowed d-d transitions of the low-spin 3d⁶ cobalt(III) and a charge-transfer NH₂pao⁻ → Fe^III band. The δ and ΔΕ_Q ⁵⁷Fe-Mössbauer parameter of 1 at 80 K show the presence of an isolated high-spin Fe^III center. Variable-temperature (1.8 K–300 K) and variable-field (0–7 T) magnetic studies confirm the isolated character of Fe^III. A critical discussion of the importance of NH₂paoH and its anionic forms (NH₂pao⁻, NHpao²⁻) in homo- and heterometallic chemistry is also attempted. Full article

Vibration spectroscopy is routinely used in analytical chemistry for molecular speciation. Less common is its use in studying the dynamics of reaction and transport processes. A shortcoming of vibration spectroscopies is that they are not inherently specific to chemical elements. Progress in synchrotron radiation-based X-ray technology has developed nuclear resonance vibration spectroscopy (NRVS), which can be used to produce element-specific vibration spectra and partial vibrational density of states (PVDOS), provided the material under investigation contains a Mössbauer-active element. While the method has been recently used successfully for protein spectroscopy, fewer studies have been conducted for condensed matter. We have employed NRVS on the BaSnO₃ perovskite structure, which is a model compound for ceramic proton conductors in intermediate temperature fuel cells. Since we used ¹¹⁹Sn as a Mössbauer isotope, the derived experimental PVDOS is specific to the element Sn in BaSnO₃. We show how this phonon DOS is used as an experimental anchor for the interpretation of the DFT-calculated PVDOS of BaSnO₃. Full article

Mössbauer spectroscopy can be advantageous for studying catalysts. In particular, its use in in situ studies can provide unique access to structural features. However, special attention must be paid to the interpretation of data, since in most studies, the samples are not perfectly homogeneous. Balance and compromise should be found between the refinement of evaluations by extracting and interpreting data from spectra, while also considering the presence of possible inhomogeneities in samples. In this review, examples of studies on two types of catalysts are presented, from which, despite possible inhomogeneities, clear statements can be derived. The first example pertains to selected iron-containing microporous zeolites (with ⁵⁷Fe Mössbauer spectroscopy), from which unique information is collected on the coordination of iron ions. The second example is related to studies on supported PtSn alloy particles (with ¹¹⁹Sn probe nuclei), from which reversible modifications of the tin component due to interactions with the reaction partners are revealed. Full article

Nanoparticles of ZnFe₂O₄ and hematite with varied sizes and distributions were synthesized using the two-solvent method (cyclohexane, water) on SBA-15 silica batches. Calcination is performed in air at 700 °C (2 °C/min) with rapid quenching produced catalysts with distinct nanoparticle configurations, namely, internal zinc ferrite and external hematite. The choice of precursor was critical, and nitrate salts yielded only zinc ferrite nanoparticles, while chloride salts produced a mixture of hematite and zinc ferrite. The photocatalytic activity of these materials was evaluated under visible light irradiation from an LED lamp, using O₂ from air as an oxidizing agent without the addition of H₂O₂. Samples enriched with external hematite nanoparticles from chloride precursors achieved the highest activity, decomposing 30% of AMX in 225 min. In contrast, nitrate-derived samples with predominantly internal zinc ferrite nanoparticles exhibited lower catalytic activity. Characterization via TEM, XRD, N2 sorption, and Mössbauer spectroscopy confirmed the structural and magnetic properties of the nanoparticles. Mössbauer spectra, particularly at 12K and under a magnetic field, demonstrated the presence of hematite nanoparticles, distinguishing them from isolated Fe (III) cations. Zinc ferrite nanoparticles exhibited specific magnetic ordering, with Fe ions occupying tetrahedral and octahedral sites. The results demonstrate the critical role of nanoparticle, composition, and positioning in optimizing photocatalytic efficiency for water decomposition. Full article

Zinc-substituted cobalt ferrites were obtained by a green method using a black grape extract as a reductant and fuel. XRD analysis confirmed the spinel structure of the synthesized ferrites. An increase in the lattice constant is explained by increased Zn content. SEM analysis confirmed changes in surface morphology, whereas FTIR spectra demonstrated the presence of organic species in the samples, which originated from grape extract. The content of Co(II) ions in octahedral sites as a function of the ratio between Fe(III) ions in A- and B-sites was calculated from Mössbauer data. pH_PZC rose from 7.85 to 8.13 with an increase in zinc content, indicating a positive charge of the adsorbent surface at natural pH. The adsorption–catalytic properties of the spinel samples were investigated in terms of Congo Red (CR) dye removal. The mechanism of CR adsorption on the ferrite surface includes electrostatic and donor–acceptor interactions with the adsorbent surface. Furthermore, the sample with x(Zn) = 0.4 exhibited the highest degradation rate constant k = 0.102 min⁻¹ in the peroxide oxidation of CR, whereas the sample with x(Zn) = 1.0 exhibited the highest adsorption capacity. The electron transfer between ferrite samples and hydrogen peroxide was evidenced using electrochemical tests. The green-synthesized Co-Zn ferrites demonstrate a big potential as adsorbents/catalysts for water treatment. Full article

The effect of the Mn³⁺ ion on the local distortions of FeO₆ octahedra in orthoferrite samples was investigated. Mössbauer spectroscopy measurements for a series of ${\mathrm{HoFe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{O}}_3$ (x = 0–0.7) orthoferrite samples with the space group Pnma were carried out at temperatures above the Néel point (700 K). The electric field gradient (EFG) tensor on Fe ions for these compounds was found using first-principle calculations. The concentration dependence of quadrupole splitting was obtained using experimental and theoretical data. Mn³⁺ cations were found to affect the Mössbauer spectra mainly due to distortions of the crystal lattice. Theoretical calculations show that the values of all electric field gradient components increase significantly with the manganese concentration in the system, and the eigenvectors ${\mathbf{e}}_{\mathbf{xx}}$ and ${\mathbf{e}}_{\mathbf{yy}}$ of the electric field gradient tensor sharply change their direction at concentrations of x > 0.1. Full article

The chemistry of heterometallic metal complexes continues to attract the interest of molecular inorganic chemists mainly because of the properties that different metal ions can bring to compounds. Contrary to the plethora of 3d–4f- and 3d–3d′-metal complexes, complexes containing both 3d- and 4d-metal ions are much less studied. The choice of the bridging organic ligand is of paramount importance for the synthesis of such species. In the present work, we describe the use of the potentially tetradentate NOO′O″ Schiff bases N-(2-carboxyphenyl)salicylideneimine (saphHCOOH) and N-(4-chloro-carboxyphenyl)salicylideneimine (4ClsaphHCOOH) in Cd^II-M^III (M = Fe, Cr) chemistry. The complexes [Cd₂Fe₂(saphCOO)₄(NO₃)₂(H₂O)₂] (1), [Cd₂Cr₂(saphCOO)₄(NO₃)₂(H₂O)₂] (2), [Cd₂Fe₂(4ClsaphCOO)₄(NO₃)₂(H₂O)₂] (3) and [CdCr₂(4ClsaphCOO)₄(H₂O)₃(EtOH)] (4) have been structurally characterized, the quality of the structure of the latter being poor but, permitting the knowledge of the connectivity and the main structural features. Complexes 1–3 are isostructural, but not isomorphous, possessing a variety of lattice solvent molecules (EtOH, MeCN, CH₂Cl₂, H₂O). The metal topology can be described as two isosceles triangles sharing a common Cd^II…Cd^II edge. The two Cd^II atoms are doubly bridged by two μ-aqua groups. The M^III…Cd^II sides of the triangles are each asymmetrically bridged by one carboxylate oxygen atom of a 2.2111 saphCOO²⁻/4ClsaphCOO²⁻ ligand. The core of the molecules is {Cd₂M₂(μ-O_aqua)₂(μ-OR)₄}⁶⁺, where the OR oxygen atoms are the bridging carboxylate oxygens. The coordination spheres of the metal ions in the centrosymmetric molecules are [Cd(O_aqua)₂(O_carboxylato)₄(O_nitrato)₂] and [M(N_imino)₂(O_carboxylato)₂(O_phenolato)₂]. The biaugmented trigonal prism is the most appropriate for the description of the coordination geometry of the Cd^II atoms in 1 and 3, while the geometry of these metal ions in 2 is best described as distorted triangular dodecahedral. A combination of H-bonding and π–π stacking interactions give interesting supramolecular patterns in the three tetranuclear compounds. The three metal ions in 4 define an isosceles triangle with two almost equal Cd^II…Cr^III sides. The Cd^II center is linked to each Cr^III atom through one carboxylato oxygen of a 2.2111 4ClsaphCOO²⁻ ligand. The core of the molecule is {CdCr₂(μ-OR)₂}⁶⁺, where the OR oxygen atoms are the bridging carboxylato oxygens. A tridentate chelating 1.1101 4ClsaphCOO²⁻ ligand is bonded to each Cr^III. The coordination spheres are [Cd(O_aqua)₃(O_ethanol)(O_{bridging carboxylato})₂(O_{terminal carboxylate})₂] and [Cr(O_{bridging carboxylato})(O_{terminal carboxylato})(O_phenolato)₂(N_imino)₂]. Complexes 1–4 are the first heterometallic 3d–4d complexes based on saphHCOOH and 4ClsaphCOOH. The structures are critically compared with those of previous reported Zn^II-M^III (M = Fe, Cr) complexes. The IR and Raman spectra of the complexes are discussed in terms of the coordination modes of the ligands involved. UV/VIS spectra in CH₂Cl₂ are also reported, and the bands are assigned to the corresponding transitions. The δ and ΔE_Q⁵⁷Fe-Mössbauer parameters of 1 and 3 at room temperature and 80 K suggest the presence of isolated high-spin Fe^III centers. Variable-temperature (1.8–310 K) and variable-field (0–50 kOe) magnetic studies for 1 and 2 indicate the absence of M^III…M^III exchange interactions, in agreement with the long distances (~8 Å) between the paramagnetic metal ions. The combined work demonstrates the ability of saphCOO²⁻ and 4ClsaphCOO²⁻ to give 3d–4d metal complexes. Full article

In this study LiFePO₄/C composite particles were synthesized using five different carbon sources via a one-step sol-gel method. La-doped LiFePO₄ was also synthesized using the sol-gel method. The XRD pattern of Li_xLa_yFePO₄ (x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h indicates that as the doping ratio increased, the sample’s cell volume first increased then decreased, reaching a maximum value of 293.36 ų (x = 0.94, y = 0.06). The XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at different temperatures for 10 h indicate that with increasing calcination temperature, the (311) diffraction peak drifted toward a smaller diffraction angle. Similarly, the XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at 700 °C for different durations indicate that with increasing calcination times, the (311) diffraction peak drifted toward a larger diffraction angle. The infrared spectrum pattern of Li_xLa_yFePO₄ (x = 0.9~1.0, y = 0~0.1) after being calcined at 700 °C for 10 h shows absorption peaks corresponding to the vibrations of the Li–O bond and PO₄^3- group. An SEM analysis of Li_xLa_yFePO₄ (x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicates that the particles were irregular in shape and of uniform size. The hysteresis loops of Li_0.92La_0.08FePO₄ after being calcined at 600 °C, 700 °C, or 800 °C for 10 h indicate that with increasing calcination temperature, the Ms gradually increased, while the Mr and Hc decreased, with minimum values of 0.08 emu/g and 58.21 Oe, respectively. The Mössbauer spectra of Li_xLa_yFePO₄ (x = 1, y = 0; x = 0.96, y = 0.04; x = 0.92, y = 0.08) after being calcined at 700 °C for 10 h indicate that all samples contained Doublet(1) and Doublet(2) peaks, dominated by Fe²⁺ compounds. The proportions of Fe²⁺ were 85.5% (x = 1, y = 0), 89.9% (x = 0.96, y = 0.04), and 96.0% (x = 0.92, y = 0.08). The maximum IS and QS of Doublet(1) for the three samples were 1.224 mm/s and 2.956 mm/s, respectively. Full article

Studies of the mineralogical composition were carried out, and the features of the clays from the deposits of Kazakhstan were established using Mössbauer spectroscopy (MS) and X-ray diffraction analysis (XRD). According to the XRD results, all the samples were mixed-layer clays of the kaolinite–illite type. The lattice parameters of the kaolinite were determined, and it was shown that its structure was disordered and contained a certain amount of impurity in some of the clay samples. A special feature of two of the samples was the additionally identified muscovite polytype 2M₁. The spectra of the iron-containing clays were amenable to being resolved into separate components, with similar Mössbauer parameters of the kaolinite, muscovite, illite, and glauconite. The oxidation state of the iron was determined using MS. The predominant part of paramagnetic iron in most samples was in the trivalent state. The primary minerals contributing to Fe²⁺ were illite and muscovite. The results obtained during the study of the clay samples with complex mineralogical compositions using MS and XRD methods both complemented one another and were found to be in good agreement. Full article

Fe₇₈B₁₅Sn₇ and (Fe₃Co₁)₇₈B₁₅Sn₇ amorphous metallic alloys were prepared using the method of planar flow casting. The amorphous nature of ribbons containing 7 at. % Sn was verified by X-ray diffraction. The resulting chemical composition was checked by flame atomic absorption spectroscopy and by mass spectrometry with inductively coupled plasma. The microstructure of the as-quenched metallic glasses was investigated by 57-Fe and 119-Sn Mössbauer spectrometry. The experiments were performed with transmission geometry at 300 K, 100 K, and 4.2 K, and in an external magnetic field of 6 T. The replacement of a quarter of the Fe by Co did not cause significant modifications of the hyperfine interactions in the 57-Fe nuclei. The observed minor variations in the local magnetic microstructure were attributed to alterations in the topological short-range order. However, the in-field 57-Fe Mössbauer spectra indicated a misalignment of the partial magnetic moments. On the other hand, the presence of Co considerably affected the local magnetic microstructure of the 119-Sn nuclei. This was probably due to the higher magnetic moment of Co, which induces transfer fields and polarization effects on the diamagnetic Sn atoms. Full article