Search

Compounds that exhibit the spin crossover effect are known to show a change of spin states through external stimuli. This reversible switching of spin states is accompanied by a change of the properties of the compound. Complexes, like iron (II)-triazole complexes, that exhibit this behavior at ambient temperature are often discussed for potential applications. In previous studies we synthesized iron (II)-triazole complexes and implemented them into electrospun nanofibers. We used Mössbauer spectroscopy in first studies to prove a successful implementation with maintaining spin crossover properties. Further studies from us showed that it is possible to use different electrospinning methods to either do a implementation or a deposition of the synthesized solid SCO material into or onto the polymer nanofibers. We now used a solvent in which both, the used iron (II)-triazole complex [Fe(atrz)3](2 ns)2 and three different polymers (Polyacrylonitrile, Polymethylmethacrylate and Polyvinylpyrrolidone), are soluble. This shall lead to a higher homogeneous distribution of the complex along the nanofibers. Mössbauer spectroscopy and other measurements are therefore in use to show a successful implementation without any significant changes to the complex. [ABSTRACT FROM AUTHOR]

Nanoparticles of cobalt ferrite are doped with multiple lanthanum (La) amounts up to an unusually high level of doping. They are synthesised using a soft chemical approach. The structural characterisation is conducted using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystallite size, micro strain, crystal density, deformation and twin fault probability are found out by Rietveld analysis. Room temperature Mössbauer spectroscopy is performed for determination of spin aberration due to La doping. The values of isomeric shift are obtained in the range of 0.33–0.41 mm/s for different samples as compared to the standard range of 0.32–0.34 mm/s. Large and narrow hysteresis are observed in 5 K and 300 K magnetic measurements, respectively with coercivities in the range 0.2–2 kOe at room temperature. The coercivity is in the range of 0.8–15 kOe at 5 K. The results from magnetic measurement show deviation from standard which is also seen from the inferences from Photoluminescence (PL) which hint at the increased versatility of the ferrite material by doping with rare earth (RE) metals. However, there is an upper limit to this inclusion in the ferrite matrix. As such there is also the existence of wasp-waist hysteresis which is indicative of antiferromagnetic (AFM) to ferromagnetic (FM) interaction but from the Rietveld analysis it is seen that this coupling does not have an undesirable effect on the stability of the nanoferrite. [ABSTRACT FROM AUTHOR]

Ni0.65Zn0.35AlxFe2−xO4 that has been synthesized using a solution-gelation method and calcined at 600 °C for 4 h was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A single-phase cubic spinel structure belonging to the Fd-3 m space group was confirmed by Rietveld refinement. The cation distribution that was anticipated using the XRD data deviated from the preferential occupancy, and the results of the magnetization analysis supported this. The two absorption bands in the FTIR spectra corresponding to the tetrahedral and octahedral sites further support the establishment of the ferrite skeleton. Al3+ doping was found to have a considerable impact on the Debye temperature, bulk modulus, and stiffness modulus measured using FTIR data. Interatomic bonding became stronger, increasing elastic moduli. The morphology was examined using SEM, whose results showed a cluster of grains. Additionally, spherical nanoparticles with an average size of 28 nm were visible in the TEM image, which is in good agreement with the crystallite size given by the Williamson-Hall method. The Mössbauer analysis and M–H data showed a soft magnetic behavior with coercivity fluctuation. According to Arrhenius plots, all samples displayed a semiconducting characteristic. With Al3+ doping, dielectric studies revealed a declining trend. [ABSTRACT FROM AUTHOR]

The solid-state reaction technique was used to produce polycrystalline Bi1−xBaxFe1−x(Zn1/3Nb2/3)xO3 at different substitutions for x = 0, 0.025 and 0.05 (referred to as BFO, BBFZN25, and BBFZN50, respectively). Both x-ray diffraction and Raman spectroscopy revealed that the substitution did not affect the rhombohedral structure of BFO. However, the substitution did not prevent the formation of a second phase, which was identified as Bi25FeO39. The amount of this impurity phase was extracted through Rietveld refinement and was further corroborated by Mössbauer spectroscopy. Lattice parameters were found to be increased owing to substitution of larger ions on average. The substitution not only had an impact on average crystallite size, microstrain and dislocation density of BFO, but also had a significant effect on its dielectric properties. As a result, the dielectric permittivity was enhanced, with a notable reduction in dielectric loss. In particular, the magnitude of dielectric permittivity for the optimal composition BBFZN25 reached a value of 360 at room temperature (RT), which is much greater than that for pure BFO. This higher dielectric constant may be attributable to the larger average crystallite size. The reduction in dielectric loss, at RT, suggests an improvement in the electrical resistivity of BFO, caused by the reduction of the creation of oxygen vacancies and the generation of Fe2+. The non-formation of Fe2+ was verified through Mössbauer spectroscopy. The remarkable increase in the dielectric constant for BBFZN25 at higher temperatures (T > RT) is attributed to the interfacial polarization occurring at grain–grain boundary and internal barrier layers related to the Bi25FeO39 phase. [ABSTRACT FROM AUTHOR]

The effect of thermal treatment on the structural arrangement and pore size distribution in NiFe2O4/reduced graphene oxide composite materials has been studied using X-ray diffraction, Mössbauer spectroscopy, and nitrogen adsorption/desorption technique. Composite materials have been successfully synthesized by the joint hydrothermal method using graphene oxide colloidal solution obtained by the modified Tour method. The electrical properties of the composite materials, as well as the pure component, have been studied in the frequency range from 0.1 Hz to 1 MHz, in the temperature range from 25 to 175 °C using impedance spectroscopy. A synergetic increase in the electrical conductivity of composite materials compared to pure components has been observed. The activation energies of interparticle hopping of charge carriers have been calculated using Arrhenius-type conductivity plots. [ABSTRACT FROM AUTHOR]

We explore the solventless synthesis of iron oxide nanomaterials obtained on thermal conversion of iron(III)citrate in presence of malonic acid and glucose as co-precursors in varying weight ratios and physical characterization of the materials obtained. Pure phase of hematite was found only for a particular combination of precursor and co-precursor and else a mixture of hematite and magnetite. Significant effect of the co-precursors on the nature and size of the synthesized materials was noticed. Gradual conversion of hematite to magnetite with increasing amount of co-precursor was established. Morin transition was observed in the temperature dependent magnetization study for the hematite materials. Absorption spectroscopy exhibited three different electronic transitions that take place within the 3d5 shell of the octahedrally coordinated Fe3+ ions for hematite materials. The optical (direct and indirect) band gaps estimated from the Tauc's plot showed particle size dependence. From photoluminescence study the transitions of trapped electrons in various defect states of oxygen vacancies were observed which led to the appearance of nonradiative peaks. In the Raman spectra the significant bands of hematite (A1g and Eg bands) were noted. From morphology study the hematite nanomaterials appear as clusters of large irregular shaped particles of various sizes. Formation of hematite nanomaterials as observed by XRD studies was supplemented by the SAED patterns obtained in the HRTEM study. Present study established that nano-sized pure hematite materials can be thermally synthesized at comparatively lower temperature on thermal decomposition of iron(III)citrate by varying the weight ratio of suitable co-precursors. [ABSTRACT FROM AUTHOR]

Ubiquitous nanomaterials have been extensively involved in multifarious biotransformation of diverse organic and synthetic techniques. This research study describes the robust immobilization of α-amylase on magnetic nanoparticles of magnesium ferrite (MgFO) functionalized with silane. The XRD patterns, FESEM and HRTEM images were analysed to study structural and morphological features. The crystallite size of MgFO is found to be 12 nm. The FTIR results confirmed the covalent attachment of the enzyme with the MgFO and VSM and Mössbauer spectrometric graphs were evaluated to study the magnetic behaviour of the prepared samples. The Kinetic parameters, reusability, storage capacity and catalytic activity of the enzyme at various reaction time, pH and temperature conditions before and after attachment with MgFO were examined to confirm the successful immobilization process. The reusability of the enzyme on modified MgFO is found to be good (> 50%) even after 12 consecutive usability cycles and also retain 50% catalytic efficiency over 30 days storage period. [ABSTRACT FROM AUTHOR]

The effects of the addition of mango residue on the combustion of iron nitrate–urea mixtures are presented herein. The process was performed considering two systems: open (porcelain capsule) and closed (round-bottom flask), both with and without the addition of the residue, thus resulting in four different products. Thermogravimetric techniques (thermogravimetric analysis and differential thermal analysis) were used to assess the thermal behavior of the precursors, X-ray diffraction, Mossbauer spectroscopy and spectrometry in the infrared region with Fourier transform to analyze the influence of the synthesis parameters on the structure of the products, scanning electron microscopy, surface area, and porosity analysis, to analyze the morphology and textural properties of the samples. The addition of mango residue to either system caused changes in the combustion process, iron oxide phase, morphology, textural properties, and, particularly, the specific surface area in the closed system-produced material, in which a significant increase was observed. Thus, the addition of mango residue in the combustion synthesis of iron oxides can increase the added value of waste materials, thereby producing favorable economic and environmental impacts. [ABSTRACT FROM AUTHOR]

Egyptian granite was used in preparing some glass samples including different contents of sodium carbonate as a fluksing agent and to study the effect of different Na+ ions on some of their properties. The prepared glass samples have the chemical composition [100 -x granite.xNa2CO3, Where x = 11, 12, 13, 14 and 15 mol%]. The mixture of each sample was mixed well and prepared in a platinum crucible at 1430 °C for one hour, then quenched in air between two copper plates. The as prepared glass samples were investigated by XRD, FTIR, Mössbauer spectrometer, d.c. and a.c. conductivities. XRD results showed that the prepared samples have the glassy nature. FTIR results showed approximately similar de-convoluted bands. The identification of these bands revealed that the present vibration modes in these samples were Si-O-Si bending vibration, Si-O-Al stretching and Si-O-Si symmetric, Si-O− and Si-O-Si asymmetric stretching. Mössbauer results revealed that the granite spectrum showed two magnetic sites [Fe3O4 (Fe III) A site and Fe3O4 (Fe II, III) B site]. And also another two doublets represented Fe (II) and Fe (III). The glass samples spectra showed two doublets represented Fe2+ and Fe3+ (Oh). The a.c. conductivity at low temperature for the glass samples showed week temperature dependence and strong frequency dependence. At high temperature the behavior reversed. The a.c. behavior showed also that the relation of ln(σ) and 1/T of each glass sample exhibited one line with two slopes. This reflects that the electric conduction is due to ionic and electronic conduction. The behavior of the relation between Na+ content and ln(σ) showed the behavior of the extrinsic semiconductor at low temperature range where the pentavalent or trivalent ions of silicon matrix changed their electrical features producing p-type and n-type semiconductors respectively. The dielectric constant (ε') showed fixed values up to a certain temperature, then ε' started to increase gradually with inversely proportional to frequency. [ABSTRACT FROM AUTHOR]

Carbonatite is an igneous rock that is composed mainly of carbonate minerals and silicates. It is recently applied as fertilizer due to its high content of calcite and dolomite. This study presents a physical and chemical characterization of the Spanish River Carbonatite (SRC) and its application as fertilizer is tested. The chemical composition obtained by X-ray fluorescence and Energy Dispersive X-ray analyses indicates that Ca, Fe and Si are the main contained elements. Calcite and SiO2 are the principal mineralogical phases as detected by X-ray diffraction. Fourier transform infrared spectroscopy confirms the presence of calcite, silicates and also organic material and water. It also suggests the presence of vermiculite. Thermal analysis reveals only a one-step reaction that corresponds to the decomposition of calcite. Mössbauer spectroscopy performed at room temperature do not show magnetic order between the iron moments instead it shows Fe2+ and Fe3+ doublets in M1 and M2 octahedral sites belonging to vermiculite. At 50 K, we observe that the isomer shift increases their values due to the second order Doppler shift. SQUID magnetometry measurements reveal that most of the sample contains paramagnetic domains assigned to the silicates and calcite components. However, under low applied fields, a tiny signal for Verwey transition appears at 124 K (suggesting the presence of magnetite) although screened by the strong paramagnetic signal of the main components. The SRC has been tested as potential fertilizer on sweet cucumber (Solanum muricatum) which responded positively to the application to carbonatite as an amendment, expressing itself in high foliar biomass. [ABSTRACT FROM AUTHOR]

Nitriding of austenitic stainless steel (ASS) causes changes to its surface, and it is widely used in technological applications. The extreme sensitivity of the formed layer not only to the nitriding process but also to its parameters (or nitriding conditions) leads to an infinite number of samples, making it difficult to compare it with results from different authors. The nitrided layer has a gradient of the nitrogen content profile. This, added to the presence of non-stoichiometric phases and the presence of induced residual stress, forms a very heterogenous probed area. Another issue is that despite being relatively well studied, the crystallographic structure of the expanded austenite, which is the main structure formed, is not well established. Considering this, many challenges remain concerning the characterization of the microstructure of the formed layer, mainly because of the limitations of the local structure characterization tools, whose results can be extremely difficult to interpret. Moreover, recent results suggest that the surface proximity may substantially affect the structure in this outermost region, and therefore even a few tenths of a micron must be carefully characterized, which increases the complexity of this system. In this context, Mössbauer spectroscopy (MS) is an interesting exploratory technique, which, if correlated with other techniques, can support this challenging task. However, regardless of the intrinsic complexity of this spectroscopy, interpreting the Mössbauer spectrum is not straightforward, requiring not only a solid understanding of the nitrided ASS system, but also a careful correlation with the results of other techniques. In this study, these points are cautiously detailed and the implications in the MS analyses are widely discussed. Finally, some ways of improving the analyses are outlined and discussed. [ABSTRACT FROM AUTHOR]

Jeffbenite, ideally Mg3Al2Si3O12, has been identified as inclusions in super-deep diamonds originating from depths that exceed 300 km. Although Mg-end member jeffbenite has limited stability at upper-mantle conditions, iron-bearing jeffbenite may have broader P–T stability that extends to the transition zone or uppermost lower mantle, incorporating significant amounts of ferric iron. Using synchrotron-based, single-crystal X-ray diffraction (XRD) and synchrotron Mössbauer spectroscopy (SMS) at pressures up to 29 GPa, we report the crystal structure, compressibility, and likely spin transition of iron in ferromagnesian jeffbenite (Mg2.32Al0.03Fe2+1.28Fe3+1.77Si2.85O12). High-pressure structure refinements reveal that Fe3+ substitution for Si in the T2 site, which shares edges with the M2 octahedron, likely stabilizes jeffbenite at high pressure, because it increases the cation-to-cation distance between these sites. Although ferromagnesian jeffbenite does not undergo a structural phase transition below 30 GPa, SMS hyperfine parameters suggest the onset of an electronic spin transition of iron from high-spin (HS) to low-spin (LS) at around 22 GPa, which may increase its stability at high pressures. Pressure–volume data were fit to a third order Birch–Murnaghan equation of state, resulting in V0 = 816.54(9), KT0 = 181.54(1.39), and K T 0 ′ = 2.76(14). These equation of state parameters are applicable to evaluating the encapsulation pressures of super-deep diamonds. The density and bulk modulus of ferromagnesian jeffbenite are similar to or higher than pyrope–almandine, pyrope–majorite, and skiagite–majorite solid solution garnets, further suggesting that jeffbenite may be an important ferric–iron silicate in the deeper parts of the mantle transition zone and uppermost lower mantle. However, future studies on the influence of temperature and oxidation state on the stability and equations of state of iron-bearing jeffbennite are still needed to determine what role, if any, jeffbenite plays in transition-zone mineralogy. [ABSTRACT FROM AUTHOR]

Mössbauer spectra of Feridex, an MRI enhancement agent, show that it contains superparamagnetic γ-Fe2O3 nanoparticles. From spectra in magnetic fields applied at room temperature the magnetic moment of the particles was measured to be 11,250 μB, from which the diameters of the single-domain particles are estimated to be about 8 nm. This is smaller than the hydrodynamic particle size of 30 nm which includes a protective coating of dextran. The particles are monodisperse, as shown by the continuous change from a broad superparamagnetic line to a magnetic 6-line pattern as the temperature is lowered below the blocking temperature TB of about 90 K. The magnetic moments and blocking temperature are consistent with those of γ-Fe2O3 samples of known sizes. [ABSTRACT FROM AUTHOR]

Enzymes and protein's immobilization on magnetic nano supports is emerging as a promising candidate in the food, medical field, and areas of environmental studies. This work presents a study on purified Bacillus thermoamylovorans lipase (BTL) by utilizing tetraethoxysilane (TEOS)-modified magnesium nano ferrite (MgNF) of 20 nm size. Its structural and morphological studies were investigated by powder X-ray diffractometry, high-resolution transmission electron microscopy, etc. Binding of BTL with MgNF was supported by using Fourier transform infrared spectroscopy. Magnetic behavior was examined by the vibrational sample magnetometer and Mössbauer spectrometer graphs. The enzymatic activity of BTL before and after immobilization was studied at different temperatures and reaction time. As per the Lineweaver-Burk plot, immobilized lipase has more biological affinity for fatty acids in comparison to the free lipase, and Kmax values of immobilized and free BTL were computed as 6.6 and 7.5 mM respectively, with excellent reusability(> 50%) even till 13 consecutive assay runs. [ABSTRACT FROM AUTHOR]

In this investigation, we have used the thermal treatment method for the preparation of nickel and manganese ferrite nanoparticles. All the samples were calcined at different temperatures from 420 to 570 °C. The results of XRD demonstrated the variation of average nanocrystallite size as a function of calcination temperature. Mossbauer spectra of calcined NiFe2O4 nanoparticles at 570 °C exhibit two sextets, indicating the samples are ferromagnetic, while calcined MnFe2O4 nanoparticles at 420 °C reveal simultaneous presence of two paramagnetic doublets with a central magnetic sextet. The Mossbauer spectroscopy is also applied here for investigating the magnetic hyperfine characteristics and cation distribution of the above-mentioned ferrite nanoparticles. Mossbauer results demonstrate that higher calcination temperature assistances M2+ ions enter into the octahedral sites, while simultaneously Fe3+ ions transfer from the octahedral (B) sites to the tetrahedral (A) sites. As the results indicate, magnetic properties of the samples can be attributed to the hyperfine parameters such as hyperfine field and cation distribution. The results of Mossbauer showed the change in hyperfine parameters along with changing temperature and nanocrystallite size. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD), Fields Emission Scanning Electron Microscope (FE-SEM) with EDS and Mössbauer Spectroscopy (MS), were applied to investigate a newly fallen solid piece of debris named the Aba Panu meteorite, after a city in south western Nigeria (Lat: N 08° 14′ 25.7″ and Long: E 003° 33′ 47.0″). Matching X-ray diffraction results, together with the FE-SEM analysis confirms the presence of four kinds of iron-bearing minerals, namely olivine, pyroxene, kamacite (Fe-Ni alloys) and troilite (FeS). The Mössbauer spectra recorded at 295 K and 78 K consist of two strong paramagnetic doublets emanating from olivine of quadrupole splitting 2.9 mm/s and pyroxene of quadrupole splitting 2.1 mm/s. These are superimposed on two magnetic sub-spectra attributed to kamacite and troilite phases. From the Mössbauer sub-spectra absorption area, the ratio of the olivine absorption area to the pyroxene absorption area indicates that the meteorite can be classified as an L-ordinary chondrite. The mole fraction of the Fe end-member of olivine (fayalite) and the orthopyroxene (ferrosilite) calculated from the EDS data will be used to identify the petrographic type of the meteorite. [ABSTRACT FROM AUTHOR]

Sr1/3Mn1/3Co1/3Fe2O4 ferrite nanoparticles were synthesized by glycol thermal technique. The structure and morphology of the Nano ferrites were studied by X-ray powder diffraction, Fourier transform infrared FTIR, high-resolution scanning electron microscopy, and high-resolution transmission electron microscopy. The induced internal strains were investigated by Williamson plots. The results show mono-dispersive property of the sample and particle sizes that increase with increasing annealing temperature, TA. The magnetic hyperfine fields were found to be sensitive to TA as seen from room temperature 57Fe Mössbauer measurements. The magnetic hysteresis loops were performed in external magnetic field of up to 50 kOe. Room temperature M − H loops showed that the coercive fields increased to a maximum at TA of 500 °C and then decreased thereafter. Significant increases in coercive fields were observed at a measuring temperature of 4 K. Distortions in the hysteresis loops at 4 K were observed where thermal annealing effect appears to induce strong linear correlation between coercive fields and saturation magnetizations. [ABSTRACT FROM AUTHOR]

Zn/Ga/Gd-substituted NiFe2O4 was formed by solid state reaction and citrate methods. The influence of substitutions on phase formation, the strain, crystallize size, cations distribution and magnetic properties have been examined by X-ray diffraction, Mössbauer effect spectrometer, Fourier-transform infrared, and vibrating sample magnetometer. Zn/Ga/Gd substituted NiFe2O4 samples prepared by solid state method showed that as gadolinium introduced into the system, a second phase was formed with a small percentage while samples prepared by citrate method exhibited a single phase. The distributions of different cations between different sites were determined by both Mössbauer effect spectroscopy, modified Bertaut and Rietveld analysis. Mössbauer technique at room temperature showed that samples synthesized by the ceramic method have a magnetic order while samples prepared by citrate method have a superparamagnetic nature. The canting angle between magnetic ions was increased by increased the amount of Zn in samples prepared by both methods. [ABSTRACT FROM AUTHOR]

In this study, the goal was to find lower temperature for separating the Zn and Fe content of ZnFe2O4 by sulfation reaction than previously achieved and to study the various reaction steps of sulfation. Hence, the reaction of ZnFe2O4 with Mohr's salt containing iron(II), i.e., (NH4)2Fe(SO4)2·6H2O, and ammonium iron alum containing Fe(III), i.e., NH4Fe(SO4)2·12H2O, was studied. At first, the thermal decomposition of precursor salts in air was studied by TG/DTA-MS to find the proper temperature for sulfation. Then ZnFe2SO4/precursor salt mixtures with ratios 1:2 and 1:5 were prepared and annealed at 400, 425 and 450 °C. The solubility of the products obtained at different annealing temperatures in water (e.g., ZnSO4, FeSO4, Fe2(SO4)3) and in HCl (Fe2O3, ZnO, Fex(OH)ySO4, Znv(OH)wSO4 basic sulfates) was studied. The morphology and structure of the starting materials was investigated by SEM, XRD and FTIR, the crystalline phases after each annealing and washing step were studied by XRD. The Fe in the starting materials and the products obtained at 425 °C was measured by Mössbauer. Based on the obtained results, it was demonstrated that the sulfation reaction with ammonium iron sulfates could be performed at lower temperatures than with iron sulfates. It was possible to detect the reaction intermediates and to obtain information about the reaction intermediates. With our sulfation reaction, depending on the reaction conditions, it is possible to obtain Fe2O3 as final product, but the Zn and Fe metals can be obtained also as sulfates. Our results open up further possibilities to recycle the ZnFe2O4 waste material. [ABSTRACT FROM AUTHOR]

(Zn0.9Fe0.1)O powders were produced with different ball to powder weight ratios (BPR) by ball milling of ZnO and Fe elemental powders. The BPR used were 15:1, 20:1, 25:1, and 30:1. The prepared samples were studied by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy (MS). The XRD patterns showed a zinc oxide (ZnO) single phase with wurtzite structure, except for the 15:1 ratio, which exhibits an additionally bcc structure associated to α-Fe. The mean crystallite sizes were found to be around 100 Å. The Mössbauer spectra were fitted using two doublets, associated to the incorporation of Fe ions into the ZnO lattice, which correspond to the Fe3+ and Fe2+ oxidation states except for the 15:1 ratio, for which an additional sextet was necessary to obtain a good fit, this sextet was associated to segregated Fe into the sample. The increase of the BPR allowed that all Fe penetrated into the ZnO matrix. The magnetization measurement using VSM reveals that the system exhibits ferromagnetic behavior at room temperature. For sample with BPR 15:1, the ferromagnetism is due to the segregated Fe, and for higher BPRs, from 20:1 up to 30:1, we propose that their ferromagnetism is due to the percolation of polarons. These polarons appear due to the oxygen vacancies (detected by XRD) which are occupied by electrons, which appear in the charge balance. Exchange interaction between the electron spins located in the vacancies or holes and those of the magnetic impurities (Fe atoms) leads to the formation of bound magnetic polarons, which percolate, producing in this way magnetic behavior. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) often increases with the abundance of short-range-ordered iron (SRO Fe) mineral phases at local to global scales, implying a protective role for SRO Fe. However, less is known about how Fe phase composition and crystal order relate to SOM composition and turnover, which could be linked to redox alteration of Fe phases. We tested the hypothesis that the composition and turnover of mineral-associated SOM co-varied with Fe phase crystallinity and abundance across a well-characterized catena in the Luquillo Experimental Forest, Puerto Rico, using dense fractions from 30 A and B horizon soil samples. The δ13C and δ15N values of dense fractions were strongly and positively correlated (R2 = 0.75), indicating microbial transformation of plant residues with lower δ13C and δ15N values. However, comparisons of dense fraction isotope ratios with roots and particulate matter suggested a greater contribution of plant versus microbial biomass to dense fraction SOM in valleys than ridges. Similarly, diffuse reflectance infrared Fourier transform spectroscopy indicated that SOM functional groups varied significantly along the catena. These trends in dense fraction SOM composition, as well as ∆14C values indicative of turnover rates, were significantly related to Fe phase crystallinity and abundance quantified with selective extractions. Mössbauer spectroscopy conducted on independent bulk soil samples indicated that nanoscale ordered Fe oxyhydroxide phases (nano-goethite, ferrihydrite, and/or very-SRO Fe with high substitutions) dominated (66-94%) total Fe at all positions and depths, with minor additional contributions from hematite, silicate and adsorbed FeII, and ilmenite. An additional phase that could represent organic-FeIII complexes or aluminosilicate-bearing FeIII was most abundant in valley soils (17-26% of total Fe). Overall, dense fraction samples with increasingly disordered Fe phases were significantly associated with increasingly plant-derived and faster-cycling SOM, while samples with relatively more-crystalline Fe phases tended towards slower-cycling SOM with a greater microbial component. Our data suggest that counter to prevailing thought, increased SRO Fe phase abundance in dynamic redox environments could facilitate transient accumulation of litter derivatives while not necessarily promoting long-term C stabilization. [ABSTRACT FROM AUTHOR]

Using X-ray, Mössbauer, and magnetic measurements, the formation of phases has been investigated upon mechanosynthesis in a ball planetary mill and upon the subsequent annealing of samples of the cementite composition (Fe0.95-уСr0.05Niy)75C25, where у = 0-0.20, which contains two alloying elements (chromium and nickel). It has been shown that, in the mechanosynthesis process, cementite alloyed with chromium and a small amount of nickel and an amorphous phase alloyed with chromium and nickel have been formed. Upon heating above 300°С, the amorphous phase is crystallized into nickel-enriched cementite. In the process of annealing at higher temperatures, the most nickel-rich cementite decomposes with the formation of austenite. As a consequence, after annealing at medium temperatures, the composition of the alloys contains cementite alloyed mainly with chromium and some amount of alloyed austenite, which can be found in ferromagnetic or paramagnetic states depending on the Ni content. Annealing at 800°С bring about the complete or partial decomposition of cementite contained in the alloys. The intensity of the decomposition has been determined by the nickel content in the samples. [ABSTRACT FROM AUTHOR]

The series ZnxMg1-xNiFeO4(0.0≤ x ≤1.0) were prepared by the conventional solid state double sintering ceramic techniques and studied using X-ray diffraction (XRD), and Mössbauer spectroscopy techniques. The diffraction patterns of all samples show single phase cubic spinel structure. Mössbauer spectroscopy measurements at liquid nitrogen temperature show an ordered magnetic structure with well resolved tetrahedral and octahedral sites. Data analysis were performed in order to investigate the magnetic properties of the materials and their cation distribution behavior between the tetrahedral and octahedral sites. These will be discussed based on the substitution of both diamagnetic divalent. [ABSTRACT FROM AUTHOR]

We synthesised a series of Iron(II)-triazole compounds and used the electrospinning procedure to incorporate spin crossover compounds (SCO) into polylactic acid polymer fibers. Composite fiber/SCO compounds of [Fe(NH-trz)](BF) as well as [Fe(Htrz)(trz)]BF were investigated via Mössbauer spectroscopy at 293 K and 77 K. The Mössbauer studies show that the spin crossover behavior is maintained in the polymer matrix. [ABSTRACT FROM AUTHOR]

Trivalent iron sulfide (Fe S ) particles were synthesized using a modified polyol method. These particles exhibited a needle-like shape (diameter = 10-50 nm, length = 350-1000 nm) and generated a clear XRD pattern. Mössbauer spectra of the product showed a paramagnetic doublet at room temperature and distributed hyperfine magnetic splitting at low temperature. The Curie temperature of this material was determined to be approximately 60 K. The data suggest that the Fe S had a structure similar to that of maghemite ( γ-Fe O ) with a lattice constant of a = 10.6 Å. The XRD pattern calculated from this structure was in agreement with the experimental pattern and the calculated hyperfine magnetic field was also equivalent to that observed in the experimental Mössbauer spectrum. [ABSTRACT FROM AUTHOR]

Magnetic properties of perovskite oxides, SrSnFeO ( x ≤ 0.15), substituted with nonmagnetic Ca and Ti ions were studied. XRD patterns showed the orthorhombic structure (close to tetragonal) of (SrCa)(SnFe)O and Sr(SnFeTi)O. The cell volumes decreased with the increase of Ca and Ti doping rates. Although Ti-substituted Sr(Sn, Fe)O showed small saturation magnetizations as compared with non-Ti substituted one, the magnetization increased a little with Ti doping rates up to 15%. On the other hand, all Ca-substituted Sr(Sn, Fe)O showed larger saturation magnetization than non-Ca substituted one. Two doublets of Fe and a doublet of Fe were observed in Mössbauer spectra of Ca-substituted Sr(Sn, Fe)O with weak ferromagnetism, and two sextets of high spin Fe were additionally observed in Mössbauer spectra of Ca-doped Sr(Sn, Fe)O with relatively strong ferromagnetism. When Sr(Sn, Fe)O were further codoped with Ca and Ti ions, they showed the stable and enhanced ferromagnetic properties. It is considered that magnetic polarons among high spin Fe species are overlapped by shrinking or deforming the crystal structure of perovskite oxides. That is the magnetism induced by a chemical pressure of perovskite oxides. [ABSTRACT FROM AUTHOR]

We synthesised a series of seven mononuclear Schiff base coordination compounds. The symmetric pentadentate NO-donating ligands were prepared by the condensation of N-(2-aminoethyl)-1,2-ethanediamine with either 5-bromosalicylaldehyde or 5-chlorosalicylaldehyde. The octahedral coordination sphere is completed by different pseudohalide mondentate N-donating ligands. All complexes have been analysed by Mössbauer spectroscopy, ESI-MS and IR spectroscopy. The Mössbauer spectra at room temperature reveal a doublet, which are related to the high spin state (S = 5/2) of the iron(III) centres. [ABSTRACT FROM AUTHOR]

SrSnFeSbO was prepared by a sol-gel and thermal annealing method. The lattice parameters of SrSnFeSbO (x = 0.04-0.15) decreased with the increase of Fe doping rates. All samples showed ferromagnetic behavior together with a paramagnetic component, relatively strong ferromagnetism for SrSnFeSbO and SrSnFeO with Fe doping rates over 6% and 8%, respectively The Sb doping leads to the ferromagnetic behavior for the samples with the low-concentration of Fe dopant. Sn Mössbauer spectra of SrSnFeO and SrSnFeO provided a broad doublet under a magnetic field of 0.85 T. The doublet could be analyzed as a magnetic sextet with 0.76 T. In Fe Mössbauer spectra of SrSnFeO under zero and 0.85 T different line intensity ratios of two sextets were observed. It suggests that the magnetic spin structure of SrSnFeO is transversely ferrimagnetic. [ABSTRACT FROM AUTHOR]

The rigid recoil of a crystal is the accepted mechanism for the Mössbauer effect. It's at odds with the special theory of relativity which does not allow perfectly rigid bodies. The standard model of particle physics which includes QED should not allow any signals to be transmitted faster than the speed of light. If perturbation theory can be used, then the X-ray emitted in a Mössbauer decay must come from a single nuclear decay vertex at which the 4-momentum is exactly conserved in a Feynman diagram. Then the 4-momentum of the final state Mössbauer nucleus must be slightly off the mass shell. This off-shell behavior would be followed by subsequent diffusion of momentum throughout the crystal to bring the nucleus back onto the mass shell and the crystal to a final relaxed state in which it moves rigidly with the appropriate recoil velocity. This mechanism explains the Mössbauer effect at the microscopic level and reconciles it with relativity. Because off-mass-shell quantum mechanics is required, the on-mass-shell theories developed originally for the Mössbauer effect are inadequate. Another possibility is that that the recoil response involves a non-perturbative effect in the standard model which could allow for a non-local instantaneous momentum transfer between the crystal and the decay (or absorption), as proposed for example by Preparata and others in super-radiance theory. The recoil time of the crystal is probably not instantaneous, and if it could be measured, one could distinguish between various theories. An experiment is proposed in this paper to measure this time. The idea is to measure the total energy radiated due to bremsstrahlung from a charged Mössbauer crystal which has experienced a recoil. Using Larmor's formula, along with corrections to it, allows one to design an experiment. The favored idea is to use many small nano-spheres of Mössbauer-active metals, whose outer surfaces are charged. The energy radiated then varies as the charge squared divided by the recoil time. This can then be measured with the extreme sensitivity available in Mössbauer experiments. If it turns out that experiments prove the need for off-mass-shell theory, then this would have profound implications for all of condensed matter physics. It would mean that an off-mass-shell theory like those considered by Stueckelberg, Horwitz, Piron, Greenberger, and many others are required to describe nature. The inclusion of these would be a major shift in the foundations. It would mean that there are new dynamic variables-the rest masses of particles. The ability to measure the diffusion relaxation time should prove useful also in chemical analysis, and provide a new class of analytical methods for material science. This problem is also interesting because the Mössbauer effect is a phenomenon where the solid-state environment dramatically and indisputably influences the probability of a nuclear process. [ABSTRACT FROM AUTHOR]

Different aspects related to the sol-gel preparation and structural investigation of silico-phosphate glasses (SiO-PO system) doped with Fe ions are reported. During the preparation process, tetraethoxysilane was used as a precursor for SiO and phosphoric acid (HPO-HP) for PO. Ferric chloride was used as precursor for Fe ions, water as reagent for hydrolysis reaction and ethylic alcohol as solvent. The pH of the sols was modified by adding hydrochloric acid and ammonia. It was observed that a slight increase of the solution temperature (up to 40 °C) allows a drastic decrease of the gelation time (from days to hours). The structure of the obtained powders dried in air at room temperature and at 100 °C for 10 h and subsequently thermally treated at different temperatures was investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy. Vibration modes specific to Si-O-Et, Si-OH, P-O-P, P-O-Si, hydrogen bonds and HO, as well as combined modes have been observed. The local structure and electron configurations of the doping Fe ions have been investigated by Fe Mössbauer spectroscopy. Graphical Abstract: Mössbauer spectra of the sample with molar composition 0.85SiO 0.08PO 0.07FeO (Fe15) annealed at 300 °C collected at 5.7/6 K, 30 K, 60 K and at room temperature The magnetic pattern is assigned (by its hyperfine parameters) to α-FeO (36 % from total Fe, the rest being dispersed in the matrix as paramagnetic Fe with octahedral oxygen configuration). [ABSTRACT FROM AUTHOR]

The successful synthesis of nanoparticles of Fe-bearing kuramite, (Cu,Fe)SnS, is reported in this study. Nanocrystalline powders were obtained through a mild, environmentally friendly and scalable solvothermal approach, in a single run. The sample was the object of a multidisciplinary investigation, including X-ray diffraction and absorption, scanning electron microscopy and microanalysis, electron paramagnetic resonance, diffuse reflectance and Mössbauer spectroscopy as well as SQUID magnetometry. The nanoparticles consist of pure Fe-bearing kuramite, exhibiting tetragonal structure. The valence state of the metal cations was assessed to be Cu, Sn and Fe. The material presents a band gap value of 1.6 eV, which is fully compatible with solar cell applications. The uptake of Fe by nanokuramite opens a compositional field where the physical properties can be tuned. We thus foster the application of Fe-bearing nanokuramite for photovoltaics and energy storage purposes. [ABSTRACT FROM AUTHOR]

Fe Mössbauer spectroscopy has provided precise and accurate iron redox ratios Fe/Fe in ilmenite, FeTiO, found within kimberlite samples from the Catoca and Camatxia kimberlite pipes from N.E. Angola. Ilmenite is one of the key indicator minerals for diamond survival and it is also one of the iron-bearing minerals with iron naturally occurring in one or both of the oxidation states Fe and Fe. For this reason it is a good indicator for studying oxygen fugacities ( fO) in mineral samples, which can then be related to iron redox ratios, Fe/Fe. In this paper we demonstrate that the oxidation state of the ilmenite mineral inclusion from sampled kimberlite rock is a key indicator of the oxidation state of the host kimberlite assemblage, which in turn determines the genesis of diamond, grade variation and diamond quality. Ilmenite samples from the two different diamondiferous kimberlite localities (Catoca and Camatxia) in the Lucapa graben, N.E. Angola, were studied using Mössbauer spectroscopy and X-Ray Diffractometry, in order to infer the oxidation state of their source regions in the mantle, oxygen partial pressure and diamond preservation conditions. The iron redox ratios, obtained using Mössbauer spectroscopy, show that the Catoca diamond kimberlite is more oxidised than kimberlite found in the Camatxia pipe, which is associated within the same geological tectonic structure. Here we demonstrate thatFe Mössbauer spectroscopy can assist geologists and mining engineers to effectively evaluate and determine whether kimberlite deposits are economically feasible for diamond mining. [ABSTRACT FROM AUTHOR]

Zinc ferrite nano-crystals were synthesized by a microwave assisted combustion route with varying the urea to metal nitrates (U/N) molar ratio The process takes only a few minutes to obtain Zinc ferrite powders. The Effect of U/N ratio on the obtained phases, particle size, magnetization and structural properties has been investigated. The specimens were characterized by XRD, Mössbauer and VSM techniques. The sample prepared with urea/metal nitrate ratio of 1/1 was a poorly crystalline phase with very small crystallite size. A second phase is also detected in the sample. The crystallite size increases while the second phase decrease with increasing the urea ratio. The saturation magnetization and coercivity of the as prepared nano-particles changed with the change of the U/N ratio. The powder with the highest U/N ratio showed the presence of an unusually high saturation magnetization of 16 emu/g at room temperature. The crystallinity of the as prepared powder was developed by annealing the samples at 700 C and 900 C. Both the saturation magnetization ( Ms) and the remnant magnetization ( Mr) were found to be highly dependent upon the annealing temperature. Mössbauer studies show magnetic ordering in the powder even at room temperature. The Mössbauer and the magnetic parameters of this fraction are different from the standard values for bulk zinc ferrite. [ABSTRACT FROM AUTHOR]

Layered rocksalt type oxides, such as Li(NiMnCo)O, are widely used as the cathode active materials of lithium-ion rechargeable batteries. Because the nickel ions are associated with the role of the charge compensation at discharge and charge, the Ni Mössbauer measurements at 6 K using synchrotron radiation were performed to reveal the role of Ni. The Ni ions of the active materials play two roles for the redox process between the charge and discharge states of lithium-ion batteries. Half of the total Ni ions change to the low-spin Ni with Jahn-Teller distortion from the Ni ions of the discharge state. The remainder exhibit low-spin state divalent Ni ions. [ABSTRACT FROM AUTHOR]

The iron oxide FeO, the mineral magnetite sometimes called ferrosoferric oxide, is notoriousy non-stoichiometric even in bulk form so its formula may be written FeO. In nanoparticle form, where it has applications in medicine and information technology, it is even more susceptible to oxidation. In this paper we report synthesis and studies of superparamagnetic FeO nanoparticles with controlled diameters of 5.3, 10.6 and 11.9 nm. In room temperature spectra, departures from stoichiometry δ of up to 0.02 were estimated from the relative amounts of Fe / Fe and from their isomer shifts. This cannot be used for very small particles of diameter 10.6 nm and less as they are superparamagnetic at room temperature and do not show hyperfine splitting owing to fast relaxation. Such particles have promise for use in enhancing MRI signals. The magnetic spectrum is restored by the application of a relatively small magnetic field (10 kG). As the temperature is lowered the relaxation slows down and 6-line magnetic hyperfine patterns appear below a blocking temperature T. The values of T obtained are lower than those of many other researchers reported in the literature, suggesting that our particles are less affected by magnetic interactions between them. At low temperatures all the spectra are similar and closely resemble that of bulk FeO confirming that departures from stoichiometry are small. [ABSTRACT FROM AUTHOR]

Nominal compositions of In2Ti1−xTmxO5−δ, (0.0 ≤ x ≤ 0.2 and Tm = Fe3+ and Cr3+) were synthesized by ceramic route and characterized by relevant techniques. In2Ti1−xFexO5−δ samples were single phased isomorphic with In2TiO5 phase while Cr substitution has resulted in mixed phased compositions. Dynamic light scattering experiments showed the increase in proportion of smaller sized particles with the increase in extent of Fe substitution. Mössbauer spectra revealed that Fe exists in +3 oxidation state in substituted oxides. The band gap decreased from 3.2 (In2TiO5) to 2.1 eV (In2Ti0.8Fe0.2Ox−δ) and to 1.9 eV in case of Cr substitution (In2Ti0.8Cr0.2O5−δ) attributed to participation of Fe 3d/Cr 3d levels. Photocatalytic H2 generation was evaluated over the substituted oxides from water–methanol mixtures under UV–visible irradiation. The decreasing order of photocatalytic activity is as follows: 20% Fe (mol%) > 10% Fe > indium titanate ≈ 20% Cr > 10% Cr. The loading of Pt as cocatalyst on surface of most active photocatalyst, In2Ti0.8Fe0.2Ox−δ further enhanced the photocatlytic H2 yield. [ABSTRACT FROM AUTHOR]

The pseudomorphic transformation of magnetite into hematite (martitization) is widespread in geological environments, but the process and mechanism of this transformation is still not fully understood. Micro- and nano-scale techniques-scanning electron microscopy, focused ion bean transmission electron microscopy, and Raman spectroscopy-were used in combination with X-ray diffraction, Curie balance and magnetic hysteresis analyses, as well as Mössbauer spectroscopy on martite samples from a banded iron formation (2.9 Ga, Dharwar Craton, India), and from lateritic soils, which have developed on siliciclastic and volcanic rocks previously affected by metamorphic fluids (Minas Gerais, Brazil). Octahedral crystals from both samples are composed of hematite with minor patches of magnetite, but show different structures. The Indian crystals show trellis of subhedral magnetite hosting maghemite in sharp contact with interstitial hematite crystals, which suggests exsolution along parting planes. Grain boundary migrations within the hematite point to dynamic crystallization during deformation. Dislocations and fluid inclusions in hematite reflect its precipitation related to a hydrothermal event. In the Brazilian martite, dislocations are observed and maghemite occurs as Insel structures and nano-twin sets. The latter, typical for the hematite, are a transformation product from maghemite into hematite. For both samples, a deformation-induced hydrothermally driven transformation from magnetite via maghemite to hematite is proposed. The transformation from magnetite into maghemite comprises intermediate non-stoichiometric magnetite steps related to a redox process. This study shows that martite found in supergene environment may result from earlier hypogene processes. [ABSTRACT FROM AUTHOR]

Mg oxides doped with 1 % Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe in Mössbauer spectra although Fe doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe species are located at the core and shell of fine MgFeO grains and diluted in MgO matrix. [ABSTRACT FROM AUTHOR]

Mössbauer spectroscopy was used to examine Fe-containing microporous materials zeolite X and AlPO-5 designed for the reduction of Cr(VI) to Cr(III) and Cr(III) uptake. XRD, XRF, EPR and XPS were used to provide supporting information. AlPO-5 was found to only incorporate inactive Fe(III), whilst Fe(II) and Fe(III) were identified in zeolite X across a distribution of sites. Fe coordinates to oxygen atoms belonging to both water molecules and framework positions. EPR confirmed these findings and showed how the site distribution narrows upon dehydration. XPS showed that a distribution of Fe sites exists at the sample surface. Mössbauer spectroscopy was also used to track oxidation and reduction processes in Fe-zeolite X. Over time, gradual Fe oxidation takes place in air-exposed samples. Reduction under hydrogen flow increases the populations of low oxidation state Fe; as the reaction time increases, Fe(II) populations first increase, then decrease as Fe(0) is evolved. [ABSTRACT FROM AUTHOR]

A fluorozirconate glass (ZBLAN) containing BaCl nanocrystals doped with divalent Eu is a promising material for x-ray image plates for medical diagnosis. Since it is known that Eu readily oxidizes to Eu , which reduces fluorescence efficiency of the image plates, Eu Mössbauer spectroscopy was used in this work to monitor the Eu oxidation state of the samples during degradation over time in the presence of ambient humidity. In addition, Mössbauer spectroscopic experiments show that the oxidation state has already changed during the glass melt: The sample made from 5 mol% EuCl contained 78 % EuCl + 22 % EuCl deduced from the relative areas of the absorption lines. The sample made from 2.5 mol% EuCl + 2.5 mol% EuCl contained 37 % EuCl + 63 % EuCl, i.e. 26 % of the original EuCl was oxidized to EuCl . [ABSTRACT FROM AUTHOR]

Nurina-003 is a Group LL5/br Ordinary Chondrite meteorite which was recovered in the Nullarbor Desert (Australia) in 1986. The degree of weathering is classified as moderate to severe. We have characterised the Fe-bearing phases in Nurina-003 by Fe Mössbauer Spectroscopy over the temperature range 5-295 K. The spectra are dominated by Olivine and also contain Pyroxene, Troilite and a Ferric component that is (super)paramagnetic at 295 K. We clearly see the effects of the magnetic ordering of the Olivine phase in the 5 K spectrum. [ABSTRACT FROM AUTHOR]

The biosynthesis of the organometallic H cluster of [Fe-Fe] hydrogenase requires three accessory proteins, two of which (HydE and HydG) belong to the radical S-adenosylmethionine enzyme superfamily. The third, HydF, is an Fe-S protein with GTPase activity. The [4Fe-4S] cluster of HydF is bound to the polypeptide chain through only the three, conserved, cysteine residues present in the binding sequence motif CysXHisXHisCysXXCys. However, the involvement of the two highly conserved histidines as a fourth ligand for the cluster coordination is controversial. In this study, we set out to characterize further the [4Fe-4S] cluster of HydF using Mössbauer, EPR, hyperfine sublevel correlation (HYSCORE), and resonance Raman spectroscopy in order to investigate the influence of nitrogen ligands on the spectroscopic properties of [4Fe-4S] clusters. Our results show that Mössbauer, resonance Raman, and EPR spectroscopy are not able to readily discriminate between the imidazole-coordinated [4Fe-4S] cluster and the non-imidazole-bound [4Fe-4S] cluster with an exchangeable fourth ligand that is present in wild-type HydF. HYSCORE spectroscopy, on the other hand, detects the presence of an imidazole/histidine ligand on the cluster on the basis of the appearance of a specific spectral pattern in the strongly coupled region, with a coupling constant of approximately 6 MHz. We also discovered that a His-tagged version of HydF, with a hexahistidine tag at the N-terminus, has a [4Fe-4S] cluster coordinated by one histidine from the tag. This observation strongly indicates that care has to be taken in the analysis of data obtained on tagged forms of metalloproteins. [ABSTRACT FROM AUTHOR]