Mossbauer Spectroscopy Studies Research Articles

Raman and Mossbauer spectroscopy and X-ray diffractometry studies on quenched copper-ferri-aluminates.

Four spinel ferrite compositions of the CuAl(x)Fe(2-x)O4, x = 0.0, 0.2, 0.4, 0.6, system prepared by usual double-sintering ceramic route and quenched (rapid thermal cooling) from final sintering temperature (1373 K) to liquid nitrogen temperature (80 K) were investigated by employing X-ray powder diffractometry, (57)Fe Mossbauer spectroscopy, and micro-Raman spectroscopy at 300 K. The Raman spectra collected in the wavenumber range of 100-1000 cm(-1) were analyzed in a systematic manner and showed five predicted modes for the spinel structure and splitting of A1g Raman mode into two/three energy values, attributed to peaks belonging to each ion (Cu(2+), Fe(3+), and Al(3+)) in the tetrahedral positions. The suppression of lower-frequency peaks was explained on the basis of weakening in magnetic coupling and reduction in ferrimagnetic behavior as well as increase in stress induced by square bond formation on Al(3+) substitution. The enhancement in intensity, random variation of line width, and blue shift for highest frequency peak corresponding to A1g mode were observed. The ferric ion (Fe(3+)) concentration for different compositions determined from Raman spectral analysis agrees well with that deduced by means of X-ray diffraction line-intensity calculations and Mossbauer spectral analysis. An attempt was made to determine elastic and thermodynamic properties from Raman spectral analysis and elastic constants from cation distribution.

X-Ray and Infrared Studies on Superparamagnetic Ni–Zn Ferrite Nanocrystals

Series of zinc-substituted nickel ferrite, Ni1−x ZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), nanoparticles were synthesized at low temperature by using sol–gel auto-combustion method. Powder X-ray diffraction confirmed the single-spinel structure of the synthesized Ni–Zn ferrite nanocrystals with average crystallite size was found to be 30 nm which is close to that of critical size for exhibiting superparamagnetism which was further verified from Mossbauer spectroscopic studies. The stoichiometric analysis of the ferrite samples carried out by employing energy-dispersive X-ray spectroscopy is found to be as expected. Results of infrared spectroscopic studies carried out on these superparamagnetic ferrite nanocrystals are reported in this paper. The tetrahedral and octahedral absorption band frequencies suggested the spinel structure of the ferrite samples and its behavior with zinc content x is attributed to the nanosize effect and occupation of zinc cations at the octahedral [B] sites. Further, the force constants are found to be in the reported range of that for ferrites.

Fe phase complexes and their thermal stability in iron phosphate catalysts supported on silica

Comparative XRD and Mossbauer spectroscopy studies have been conducted on the effect of temperature on the phase transformations of an iron phosphate catalyst synthesized using the ammonia gel method (CAT1) and a commercial grade FePO 4 catalyst supported on silica using wet impregnation method (CAT2). The XRD patterns of both catalysts showed the presence of iron phosphate and the tridymite phase of aluminum phosphate. Mossbauer spectra of the catalysts show that the phases present in CAT1 are thermally stable up to 500 ∘C, but CAT2 shows significant changes with the tridymite phase of iron phosphate increasing from 6 % to 29 % of the spectral area at a temperature of 500 ∘C.

Magnetic and Mössbauer Spectroscopy Studies of NiFe2O4/SiO2 Nanocomposites Synthesized by Sol-Gel Method

Single-phase NiFe2O4 nanoparticles dispersed in SiO2 (30 wt %) matrix were synthesized by sol-gel method. The effects of the annealing temperature on the structural and magnetic properties of the samples were investigated at room temperature by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer, and Mossbauer spectroscopy. The samples annealed at above 800∘C exhibited single-phase cubic spinel structure. The lattice constant of NiFe2O4 increased from 0.8348 to 0.8359 nm, the saturation magnetization of the samples increased from 8.24 to 29.28 emu/g, and their coercivity increased from 23.4 to 179.0 Oe when the average grain size of NiFe2O4 in the nanocomposites increased from 6 to 40 nm with varying annealing temperatures from 800 to 1200∘C. The thickness of the dead layer on the surface of the ferrite grain was obtained to about (0.76 ±0.03) nm. The study of Mossbauer spectroscopy indicated the evolution of magnetic properties of the samples from superparamagnetic to magnetically ordered character with increasing grain size of NiFe2O4.

Effect of mechanical milling induced strain and particle size reduction on some physical properties of polycrystalline yttrium iron garnet

The effect of mechanical milling induced strain and particle size reduction on structural, micro-structural and magnetic properties of un-milled and milled polycrystalline samples of yttrium iron garnet, Y3Fe5O12 (YIG), for different duration, 3, 6, 9 and 12 h, have been studied using X-ray powder diffractometry, scanning electron microscopy, infrared spectroscopy, Mossbauer spectroscopy, high field magnetization and low field (0.5 Oe) ac susceptibility measurements. YIG on milling is found to decompose into Y3Fe5O12 and yttrium ortho-ferrite, YFeO3, phases, as reflected from various characterizations. The infrared and Mossbauer spectroscopic studies give an indication for the loss of oxygen on milling. The shift in Neel temperature with particle size reduction has been described by finite size scaling. The observed changes in M–H loop are mainly due to strain induced increase in surface anisotropy on milling. The two transitions have been observed in the thermal variation of ac susceptibility curves, corresponding to ferrimagnetic YIG-phase and another due to weak ferromagnetic YFeO3-phase.

Application Worthy SPIONs: Coated Magnetic Nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) made using magnetite (Fe 3 O 4 ) are among the various important nanosystems under active investigation for biological applications. Various characterization techniques are required to judge the quality and application worthiness of magnetic nanoparticles (NPs). Magnetite NPs were synthesized by thermal decomposition method using triethylene glycol and benzyl ether as solvents and oleic acid as surfactant with a narrow size distribution. Furthermore, magnesium oxide (MgO) is coated on these magnetite NPs to protect the magnetic nuclei from oxidation. Spherical shaped, uniformly sized, and well-dispersed NPs of ~8 ± 2 nm were studied by field emission scanning electron microscopy and high-resolution transmission electron microscopy. Cation vacancies on the surface lead to the nonmagnetic Fe 2 O 3 phase on the surface of Fe 3 O 4 NPs. MgO coated Fe 3 O 4 NPs prevented the oxidation on NP surface, which is shown through infrared, Raman and Mossbauer spectroscopy studies. Magnetization studies of oleic acid and MgO coated magnetite NPs are crucial to utilize them in biological applications. We have achieved a stable ferrofluid in nonpolar solvent using SPIONs with an average size of 8 nm for magnetic hyperthermia applications.

Magnetic Memory Effects in ${\rm Fe}/\gamma\hbox{-}{\rm Fe}_{{2}}{\rm O}_{{\bf 3}}$ Nanostructures

We report an unusual consequence of magnetic memory effect in Fe/γ-Fe2O3 nanostructures, which is prepared using an electrochemical route. Chemical phases of Fe/γ-Fe2O3 nanostructures are characterized by X-ray diffraction, optical, and Mossbauer spectroscopic studies. The static and dynamic aspects of dc magnetization studies are carried out. Thermal variation of zero-field-cooled (ZFC) magnetization displays a signature of blocking temperature (TB) at 215 K. Another broadened peak is also evident in the field-cooled (FC) magnetization at 40 K (TG). Signature of memory effect is observed below TG after cooling the sample both in ZFC and FC protocols. Appearance of memory effect in the ZFC protocol confirms spin-glass-like state below TG. Interestingly, memory effect is absent below TB even in FC protocol, although a large particle size distribution is noticed in the Fe/γ-Fe2O3 nanostructures. The results address the fundamental question whether substantial particle size distribution is sufficient enough for the memory effect in the FC protocol as found in the literatures.

XRD, Mössbauer and magnetic properties of MgxCo1−xFe2O4 nanoferrites

Abstract We report Mossbauer spectroscopy and magnetization studies of Mg x Co 1− x Fe 2 O 4 (0≤ x ≤1.0) nanoferrites. The crystallite size varies between 9 nm and 15 nm. The properties were investigated by X-ray diffraction (XRD), 57 Fe Mossbauer spectroscopy and magnetometry. The XRD results indicate pure cubic spinel structure for all the compounds. The evolution of the properties has been explained on the basis of Mg content and crystallite sizes. The Mossbauer and magnetization results show strong dependence of the properties on crystallite size and non-magnetic Mg 2+ ion concentration.

Hybrid polymer containing ferric oxides obtained using a redox polymer. Part I. Synthesis and characterization

A hybrid polymer containing hydrated iron oxide was obtained in a one-step redox process. Macroporous S/DVB copolymer containing N-chlorosulfonamide groups in Na+ form ([P]–SO2NClNa) was used as a macromolecular oxidant for Fe(II) ions which in the form of iron oxide were deposited within a polymer matrix. The final product ([P]–SO2NH2#5Fe2O3·9H2O) contained 12 % Fe(III) in the form of ferrihydrite which presence was confirmed by FT-IR and Mossbauer spectroscopic studies. The deposition of iron oxide caused reduction in BET surface and porosity of the host material.

Local and dynamic Jahn-Teller distortion in ulvöspinel Fe2TiO4

57Fe Mossbauer spectroscopic study on ulvospinel Fe2TiO4 has been conducted in a wide temperature range from 16 K to 500 K. The paramagnetic spectra are composed of several high spin Fe2 + doublets even at 500 K, which is rather strange because the point symmetry of the A-site is completely cubic (− 43m). We explain the electric field gradient (EFG) at A-site by the local arrangement of Fe2 + and Ti4 + on the B-site. The spectra were successfully analyzed by four-subspectra model, which is based on the B-site arrangement. The model also fits rather well to the magnetically ordered spectra. Thus the temperature variations of the hyperfine parameters were obtained. The Neel temperature (TN) is estimated to be about 125 K. The quadrupole coupling constants e2qQ/2 of A-site subspectra show little change around cubic-tetragonal transition temperature (Tt = 163 K), but rapidly increase below TN. From the temperature variation of line width, we found local and dynamic Jahn-Teller distortions around A-site Fe2 + ions in the cubic phase.

Hydrogen absorption characteristics and Mössbauer spectroscopic study of Ti0.67Nb0.33−xFex (x=0.00, 0.13, 0.20) alloys

Abstract The present study deals with the preparation and hydrogen absorption studies on Ti 0.67 Nb 0.33− x Fe x ( x = 0.00, 0.13, 0.20) alloys. From X-ray diffraction results it is inferred that the three alloys are bcc phase and get converted to fcc phase upon hydrogenation. Ti 0.67 Nb 0.13 Fe 0.20 alloy showed maximum hydrogen storage capacity (2.62 wt%) with fastest kinetics among the studied compositions. The hydrogenation kinetics of Ti 0.67 Nb 0.13 Fe 0.20 alloy was studied in detail over the temperature range from 298 K to 473 K. Two different types of rate equations were required to fit the kinetic data, indicating two different rate determining steps (rds) during the progress of hydriding reaction. The activation energies for the two rate determining steps have been calculated from hydrogen absorption kinetics study at different temperatures. 57 Fe Mossbauer spectroscopic study of Fe substituted alloys and their corresponding hydrides show the effect of hydrogenation on the electronic structure of the alloys in terms of electronic charge distribution and volume expansion.

Applying Mössbauer spectroscopy to studies of red blood cells in donated blood

Samples of packed red blood cells (PRBC) from standard containers for storing donated blood (35 days as per GOST) are studied. Samples for Mossbauer spectroscopy studies are taken from each container every few days over the period of storage. Analysis of the Mossbauer spectra yield data on variations in the content of different forms of hemoglobin and its derivatives in the samples studied over the storage period. Analysis of the plotted kinetic curves representing changes in the content of these forms provide estimates of the functional states of PRBC from each donor in different storage phases. Revealed distinctions in the kinetics of changes taking place in PRBC from different donors provide data on the effect of individual features of particular donors on the PRBC degradation process.

New magnetic material based on modified multi-walled carbon nanotubes and iron(III) derivatives

Magnetically active products of the interaction between the modified multi-walled carbon nanotubes, MWCNT-CO-L (L = 3-(NHCH3)C5H4N), and compounds containing FeIII ions, FeCl3·6H2O (including those with 57Fe isotopes) and trinuclear pivalate Fe2NiO(Piv)6(HPiv)3 (HPiv = HO2CCMe3), were obtained. The new substances were characterized by thermo-gravimetry combined with mass spectral analysis, Mossbauer spectroscopy, atomic absorption spectrophotometry, electron microscopy, and magnetic measurements. Based on the data of Mossbauer spectroscopy and magnetic studies, it was suggested that in the synthesized {Fe}-MWCNT-CO-L the surface of the carbon nanotubes contains nanoparticles of the polynuclear iron(III) derivatives.

Preparation and Studies on (1-x) BiFeO3–x Li0.5Fe2.5O4 (x=0.25 And 0.5) multiferroic nano-composites

Multiferroic nano-composite (1-x) BiFeO3–x Li0.5Fe2.5O4 (x=0.25 and 0.5) have been successfully synthesized by mixing the two phases, prepared independently by two different methods followed by annealing at 600 0 C. Existence of the two phases in the composite is confirmed by x-ray diffraction pattern. Average particle size is calculated to be about 45 nm for both of these phases. The saturation magnetization, remnant magnetization and coercive field increases linearly with increasing ferromagnetic phase (Li0.5Fe2.5O4) as investigated by VSM measurement. Local magnetic behaviors have been investigated by 57 Fe Mossbauer spectroscopic studies. Large dielectric constant of the order of 10 3 -10 4 has been observed in these composites. Copyright © 2013 VBRI press

Application of Mössbauer spectroscopy on corrosion products of NPP

Steam generator (SG) is generally one of the most important compo- nents at all nuclear power plants (NPP) with close impact to safe and long-term operation. Material degradation and corrosion/erosion processes are serious risks for long-term reliable operation. Steam generators of four VVER-440 units at nuclear power plants V-1 and V-2 in Jaslovske Bohunice (Slovakia) were gradually changed by new original "Bohunice" design in period 1994-1998, in order to improve corrosion resistance of SGs. Corrosion processes before and after these design and material changes in Bohunice secondary circuit were studied using Mossbauer spectroscopy during last 25 years. Innovations in the feed water pipeline design as well as material composition improvements were evaluated positively. Mossbauer spectroscopy studies of phase composition of corrosion products were performed on real specimens scrapped from water pipelines or in form of filters deposits. Newest results in our long-term corrosion study confirm good operational experiences and suitable chemical regimes (reduction environment) which results mostly in creation of magnetite (on the level 70 % or higher) and small portions of hematite, goethite or hydrooxides. Regular observation of corrosion/erosion processes is essential for keeping NPP operation on high safety level. The output from performed material analyses influences the optimisation of operating chemical regimes and it can be used in optimisation of regimes at decontamination and passivation of pipelines or secondary circuit components. It can be concluded that a longer passivation time leads more to magnetite fraction in the corrosion products composition.

Synthetic Doped Amorphous Ferrihydrite for the Fischer–Tropsch Synthesis of Alternative Fuels

Ferrihydrites (FHYDs) with the general formula of FeOOH·nH2O are naturally occurring oxyhydroxide minerals found in environments varying from river beds, lakes, and marshes to even living organisms. Here, we report the synthesis of a new kind of synthetic doped amorphous two-line FHYDs containing aluminum and copper, which are not usually known to be found in nature. Transmission electron microscopy carried out on synthetic FHYDs showed them to be amorphous in nature with some nanosized groupings in the form of nanoclusters of about 50–200 nm size without any hint of diffraction fringes associated with crystalline order. The synthetic doped FHYDs exhibit unique properties and have been characterized extensively by magnetic measurements, X-ray diffraction, and electron microscopy as well as by Mossbauer spectroscopic studies. After promotion with potassium, these FHYDs were found to have high activity as catalysts for the Fischer–Tropsch (F–T) conversion of syngas to liquid fuels over a period of ∼100 h in...

Lavras do Sul: A New Equilibrated Ordinary L5 Chondrite from Rio Grande do Sul, Brazil

The new Brazilian chondrite, Lavras do Sul, was found in 1985 at Lavras do Sul, Rio Grande do Sul State-Brazil (33°30′48″S; 53°54′65″W). It consists of a single mass weighing about 1 kg, covered by a black fusion crust with grayish interior. Four polished thin sections were prepared from a slice weighing 67 g on deposit at the Museu Nacional/UFRJ. It consists mostly of chondrules and chondrule fragments dispersed in a recrystallized matrix. Most chondrules are poorly defined and range in size from 300 to 2,000 μm, although some of them show distinct outlines, particularly when viewed under cross-polarized transmitted and reflected light. The texture of chondrules varies from non-porphyritic (e.g., barred-olivine, radial-pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine-pyroxene). The meteorite contains mainly olivine (Fa24.9), low-Ca pyroxene (Fs22.6) and metal phases, with minor amounts of plagioclase, chromite and magnetite. Mossbauer Spectroscopy studies indicate that the metal phase is kamacite, tetrataenite and antitaenite. Veins of secondary iddingsite crosscut the thin section and some ferromagnesian silicates. The chemical composition indicates that Lavras do Sul is a member of the low iron L chondrite group. The poorly delineated chondritic texture with few well-defined chondrules, the occurrence of rare clinopyroxene and plagioclase (and maskelynite) with apparent diameters ranging from 5 to 123 μm led us to classify Lavras do Sul as an equilibrated petrologic type 5. The shock features of some minerals suggest a shock stage S3, and the presence of a small amount of secondary minerals such as iddingsite and goethite, a degree of weathering W1. The meteorite name was approved by the Nomenclature Committee (Nom Com) of the Meteoritical Society (Meteoritic Bulletin No99).

Tunneling Magnetoresistance (TMR) on Fe-Al<sub>2</sub>O<sub>3</sub> Nano Granular Film Growth by Helicon Plasma Sputtering

Fe-Al 2 O 3 nanogranular thin film by helicon plasma sputtering with the variation of Fe content from 0.1 to 0.7 volume fraction have been prepared. The magnetic and magnetoresistance properties were investigated by a Vibrating Sample Magnetometer (VSM) and a Four Point Probe (FPP). The Rutherford BackScattering (RBS) was performed with the SIMNRA software. Conversion Electron Mossbauer Spectroscopy (CEMS) study was also performed to estimate the fraction of Fe and α-Fe 2 O 3 in the granular film. The results suggested that the percolation concentration occured at 0.55 Fe volume fractions, with the maximum Magnetoresistance (MR) ratio of 3%. The present MR ratio that was lower than the previous results may be related to the existence of α-Fe 2 O 3 phase.

Mössbauer spectroscopy of protein-passivated iron oxide nanoparticles

Within this work we report a Mossbauer spectroscopic study of uncoated and bovine serum albumin (BSA-) passivated magnetic iron oxide particles. Electron microscopy confirms the successful preparation of the particles with sizes in the 10 to 30 nm range. The analysis of the Mossbauer spectra at high fields shows that only 20% of the iron is present in form of Fe3O4–nanoparticles. The majority (80%) of the iron is present as maghemite (γ–Fe2O3). Coating with BSA does not influence the particle morphology and does also not affect the magnetite to maghemite ratio.

Investigation of LaFeO3 perovskite growth mechanism through mechanical ball milling of lanthanum and iron oxides

LaFeO3 perovskite was synthesized mechanochemically through ball milling of La2O3 and Fe2O3 in stoichiometric ratio. X-ray powder diffraction (XRPD), simultaneous differential scanning calorimetry and thermogravimetry analysis (DSC–TGA), Mossbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy were combined for a detailed study of the growth mechanism of LaFeO3 perovskite during the ball milling process. The XRPD results showed that La2O3 is unstable when exposed to air. Both La2O3 and La(OH)3 phases coexist under the ball milling process, indicating that La2O3 or La(OH)3 can be used to produce LaFeO3. The formation of LaFeO3 perovskite was evident after only 2 h of milling and the amount of LaFeO3 gradually increased with the increase of ball milling time. After 12 h of ball milling, single phase LaFeO3 was formed. The Mossbauer spectroscopy studies show that the spectrum of the formed LaFeO3 phase consists of three sextets and one doublet, indicating the wide distribution of LaFeO3 particle sizes and some of the smaller particles having superparamagnetic properties. This is in good agreement with the SEM images, which show that the formed LaFeO3 phase consists of nanometer-sized particles and micrometer-sized agglomerates. The formation of LaFeO3 phase was mainly caused by the La3+ substitution of Fe3+ in Fe2O3 lattice. Optical diffuse reflectance spectroscopy studies show that the formed LaFeO3 phase has semiconductor properties, with the band gap energy ~2.67 eV.