Mossbauer Effect Spectra Research Articles

Investigation of the high-temperature superconductor Tl−Ca−Ba−Cu−Fe−O in a wide range of temperature and iron concentration

A series of the composition Tl2Ca2Ba2Cu3−xFe x Oδ with 0≦x≦0.1 were prepared by the usual ceramic method. The superconducting behaviour was investigated by electrical conductivity and Mossbauer effect. X-ray diffraction on the samples was also used to study the different phases. The study revealed a superconducting transition temperature about 100 K for samples withx=0.00 and above 80 K forx=0.02 and 0.04. From the Mossbauer effect spectra measured for different compositions and at different temperatures, it is evident that the Fe ions substituted Cu into different sites. A clear evidence of vibration anisotropy is observed, together with a low spin state for each position. These results are discussed on the basis of the structure and electronic state of the compounds.

Mossbauer effect studies of Nd/sub 2/Fe/sub 14-x/Si/sub x/B and Y/sub 2/Fe/sub 14-x/Si/sub x/B

The Mossbauer effect spectra of the solid solutions of Nd/sub 2/Fe/sub 14-x/Si/sub x/B, with x equal to 0.00, 0.25, 0.50, 0.75, 1.0, 1.5, and 2.0, and Y/sub 2/Fe/sub 14-x/Si/sub x/Bi, with x equal to 0.0, 1.0, 1.5, and 2.0, have been measured at 295 K. The results are most consistent with a random distribution of the silicon over the smaller 16k/sub 1/, 16k/sub 2/, 8j/sub 1/, 4c, and 4e iron sites in Nd/sub 2/Fe/sub 14/B. Apparently, the silicon is, at least in part, excluded from the 8j/sub 2/ site, which is the site with the largest Wigner-Seitz volume. The results do not, however, rule out other possible silicon site occupancy models. The isomer shift increases slightly with increasing silicon content, whereas the quadrupole interaction remains virtually constant. The hyperfine field decreases with increasing silicon content, but the apparent linewidth increases. These changes have been modeled in terms of a distribution of hyperfine fields on each site which is determined by a binomial distribution of silicon on the Wigner-Seitz near neighbors of each iron site. >

Correlated hyperfine interactions in amorphous Cr72-xFexC17Si8Al3alloys

Fully amorphous Cr72-xFexC17Si8Al3 alloys, with 5<or=x<or=40, have been prepared by melt spinning. Room-temperature 57Fe Mossbauer effect spectra of all alloys shown an asymmetric quadrupole split doublet. These results are interpreted in terms of a distribution of Fe probe sites resulting from a distribution of near-neighbour configurations in a dense random packing model.

Goldanskii-Karyagin asymmetry in Fe3(CO)12

The Mossbauer effect spectra of Fe3(CO)12 have been measured from 4.2 to 295 K and reveal an unusual temperature dependence in the relative area of the two components of the quadrupole doublet associated with the two equivalent iron sites and in the relative area of the two observed quadrupole doublets. The asymmetry in the outer quadrupole doublet is attributed to the Goldanskii-Karyagin effect. The strong temperature dependence of the relative areas of the two quadrupole doublets results from a differing temperature dependence of the recoil free fractions for the two chemically different sites.

M�ssbauer and X-ray studies on the oxidation of annite and ferriannite

Various indirect approaches have been used to estimate the amount of the oxy end member in biotites. Since this could be used to indicate the formation temperatures and the oxygen fugacities of biotite bearing rocks, its determination requires careful experimental work. The oxidation of the iron micas annite and ferriannite has been studied by Mossbauer effect (ME) and X-ray diffraction (XRD). A model that relates ME parameters to reaction mechanism in biotites has been proposed according to which oxidation at M2 is relatively easier than oxidation at M1, a result which agrees well with the site assignment adopted. Heating synthetic ferriannite at 300° C produced an oxidation ratio that corresponds to the oxy-ferriannite end member where the ME spectra show that the two ferrous peaks are well resolved. Finally, ME and XRD results show that the c-axis decreases by 0.001 A for every percent oxybiotite added.

Structural, electrical and magnetic properties of icosahedral Al-Co alloys

Alloys of the composition Al100-xCox for x approximately=14 are found to be of the nonBravais icosahedral structure when quenched from the melt at a rate of >1*106K s-1. X-ray measurements show the presence of FCC Al as well as the icosahedral phase. Measurements on alloys of different compositions indicate that the icosahedral phase has a stoichiometry of approximately Al4Co. The 57Fe Mossbauer effect spectrum of a sample containing 1 at.% Fe shows a quadrupole split doublet. Mossbauer effect parameters are compared with those for other icosahedral Al86T13Fe (T=Cr,Mn,Fe) alloys. Magnetisation measurements show the icosahedral Al-Co alloy to be a weak paramagnet with a room-temperature susceptibility of chi =1.3*10-6 EMU g-1. The electrical resistivity shows a weak temperature dependence with a minimum at approximately 15K.

Mössbauer effect and electron spin resonance study of CdxMg1−xFe2O4 system

This work deals with the application of Mossbauer Effect (ME) in studying the crystal electric field and the cation distribution among tetrahedral (A) and the octahedral (B) sites of the spinal structure in the ferrite system Cdx Mg1−x Fe2O4 (x=0, 0.2,...1). The electron spin resonance technique (ESR) was also applied for studying this ferrite system. It was possible to characterize the ESR spectra of ferrite through the combination with the ME spectra. The ESR spectra of magnesium ferrite showed two resonance positions of Fe3+ ions and indicated that a strong exchange interaction is dominant in the pure Mg-ferrite. For high Cd concentration ferrites only single resonance line was observed. These results could be interpretted on the basis of the ME results where it indicated that Cd2+ ions prefer tetrahedral positions, forcing the Fe3+ ions from these positions to join those in the octahedral sites. The complete site occupation with different types of cations was successfully achieved from the ME spectra. The values of the quadrupole splitting indicated that for each ferrite in the system there exists an electric field gradient surrounding the Fe3+ ions in each of the octahedral and tetrahedral sites. The increase in the Mg-concentration increases the symmetry of the electric field at these sites.

An Fe Mössbauer effect study of metastable Al86Fe14prepared by rapid solidification

Icosahedral Al86Fe14 has been prepared by rapid quenching from the melt. Mossbauer effect spectra are quadrupole split doublets. The temperature dependence of the isomer shift is consistent with the second order doppler shift and the quadrupole splitting decreases linearly with temperature.

Mössbauer effect study of Li 2 1+ Me4+Fe 6 3+ O 12 2− spinels

Mossbauer effect spectra are obtained for the cubic ferrites Li2 Me Fe6 O12 (where Me4+ is one of the tetravalent elements Ge, Si and Ti) at 78K up to their magnetic transition temperatures. In a rather large temperature range they clearly are a broadened six lines pattern. Each spectrum is successfully analysed to two sets of magnetic hyperfine splitting Zeeman patterns with isomer shifts corresponding to ferric ions in both tetrahedral and octahedral sites. The tendency of the present non-magnetic elements to occupy the octahedral site led to an antiparallel Neel spin structure. Debye and Neel temperatures of these substituted lithium ferrites are determined and their hyperfine parameters are discussed.

A Mössbauer effect study of the bonding in some organoiron-copper clusters

The Mossbauer effect spectra of structurally characterized molecular metal clusters provide a valuable reference point for the identification of surface generated species important in chemisorption and catalysis. The resulting hyperfine parameters may also aid structural elucidation and provide insight into the electronic environment of the individual iron sites. We have studied in detail the clusters Na2Cu6Fe4(CO)16, Na3Cu5Fe4(CO)16, and Na3Cu3Fe3(CO)12, and several related compounds. The results indicate that the Mossbauer effect isomer shifts at 78K, which vary from −0.123 to −0.035mm/s, are very sensitive to the bonding in the molecular cluster.

Crystallization process of natural iron ores in Qatar

A very surprising anisotropy in the magnetic hyperfine interaction was observed in the Mossbauer effect spectra of some iron ore deposits in Qatar (Arabian Gulf). This was attributed to the presence of the stable as well as the metastable states of the oxyhydroxide (α-FeOOH) in the ore (glassy, mesocrystalline and holocrystalline).

Mossbauer study of the lattice dynamics of pyrite

The Mossbauer-effect spectra of a polycrystalline sample of natural pyrite (FeS2) have been measured in the temperature range 290-430K. On the basis of the centre shift and f' as a function of temperature the plus and minus second moments of frequency of the thermal vibrations of Fe atoms have been established: omega (2)=(5.68+or-0.18)*1013 and omega (-2)=(4.35+or-0.18)*1013 s-1. The ratio of these moments (1.3+or-0.1) corresponds to the Debye model with theta D=568+or-20K. The anisotropy of the Fe atom thermal vibrations at room temperature is represented by the mean-square amplitudes (z2)=(0.14+or-0.08)*10-22 m2, where the z axis is identified with the (111) crystallographic direction and (x2)=(y2)=(0.30+or-0.05)*10-22 m2. The detection of this anisotropy by the Mossbauer methods is difficult owing to the small value of the asymmetry of the lines.

Chemical ordering in Y66(FexMn1-x)34metallic glasses (Mossbauer study)

The compositional dependence of the 57Fe Mossbauer effect spectra for the metallic glasses Y66(FexMn1-x)34 has been studied. For high concentrations of Fe the spectra consist of two symmetric peaks with the spectra becoming progressively more complex as the Fe content decreases. The smooth variation of the parameters derived from the spectra indicates that Fe and Mn perform the same functions in the glass. The author finds evidence for chemical ordering in these glasses and demonstrates the existence of two distinct atomic sites for Fe. Site 1 is attributed to Fe atoms having predominantly Y near neighbours and site 2 is identified as Fe atoms having a larger number of Fe (Mn) near neighbours.

The influence of substitution of iron ions on the electron hopping in magnetite

Two commercial spinel ferrites, (Fe0.192+Mg0.562+Mn0.252+) (Fe1.873+Al0.133+)O42- and (Fe0.552+Mg0.322+Mn0.032+Cu0.102+) (Fe1.73+Al0.263+)O42-, were investigated with a view to obtaining more information about the influence of varying the proportion of Fe2+ ions on its Mossbauer effect spectra. For the first composition, for which there is a sufficient number of substituted cations for them to be located at the six nearest neighbours to Fe2+ ions, no transition between Fe2+ and Fe3+ ions occurred. On the other hand the observed broadening of the octahedral ferric spectrum for the second compound gave evidence for the electron relaxation of neighbouring Fe2+ and Fe3+ ions; this spectrum also contained a third sextet with a stronger sharp Fe2+ character. Thus it has been established that the fast electron hopping process present in this case is essentially a pair localised phenomenon. The Mossbauer effect parameters were calculated for these observed sites, and their variation with temperature discussed.

Electron spin relaxation studies of impurity iron ions in ferroelectric lithium niobate

The nuclear hyperfine structure of dilute impurity iron ions in ferroelectric lithium niobate is investigated via57Fe Mossbauer effect (ME). The ME spectra exhibit typical slow electron spin relaxation effects associated with Fe3+ ions in the6S5/2 state, which are analysed using spin-Hamiltonian formalism. For Fe3+ ions, the principal axis of EFG tensor is found to be parallel to the crystallographic c-axis. The strong external magnetic field of 47 KOe is used to study magnetic and crystal field effects on the ME hyperfine structure.

Mössbauer effect study of co-ferrite formation

The activation energy (Q) for the formation of CoFe2O4 was calculated from a series of Mossbauer effect spectra measured during the formation process. This was calculated by applying the Jander’s reaction kinetics equation to determine the reaction rate constant, on applying the Arrhenius equation. The obtained value ofQ was found to be 56 K · cal/mol.

MÖSSBAUER EFFECT STUDY OF NATURAL EGYPTIAN CHALCOPYRITE

Natural chalcopyrite samples from Umm Samuki region in Eastern Egyptian Desert were studied using Mossbauer Effect (ME) and X-ray diffraction in order to identify the different phases and phase changes occuring in the ore and to investigate the physical properties of the mineral. The ME spectra showed the existence of α, β and γ phases of chalcopyrite in addition to pyrite. The ME parameters indicated that the iron in chalcopyrite was in the trivalent state and bonded covalently. The α, β-phases were found to be in a magnetic state, while the γ phase was paramagnetic. The transformation temperature and the product of each phase was identified.

Contribution of Fe2+ions to the magnetocrystalline anisotropy constant K1of Fe3-xTixO4(0&lt;x&lt;0.1)

The magnetocrystalline anisotropy constant K1 of Fe3O4, Fe2.96Ti0.04O4 and Fe2.9Ti0.1O4 has been measured between room temperature and the Curie point using the torque method. The Fe3+ contribution to the anisotropy in this temperature range has been calculated using the theory of Wolf (1957) and the relative sublattice magnetizations determined from Mossbauer-effect spectra. The specific Fe2+ contribution, K2B1 is then found to vary with composition x and temperature T as K12B(x,T)= (0.2-3.5X) * 10-2-(0.24+3.0x)(Tc-T)10/3 * 10-8 cm-1/ion.

The Mössbauer Effect and the Anomalous Properties of the Invar Alloys

In order to investigate the cause of anomalous properties of the γ-phase iron-nickel alloys with Invar compositions, the Mossbauer effect spectra of these alloys were measured as a function of temperature. Especially, the influences of phase mixture (α+γ), cold-work and external magnetic field were examined. From these measurements, it was concluded that there exist transition states between the α and γ phases, and they cause a diversity of hyperfine fields in the Invar-type alloy. Many hyperfine fields thus produced make the Invar alloy an assembly of various magnetic transition points, which, as a result, gives rise to the anomalies of physical properties.

APPLICATION OF 129 I MOSSBAUER EFFECT TO BIOLOGICAL SYSTEMS: STUDIES WITH HEME MODELS

The Mossbauer effect associated with (129)I, (125)Te, and (57)Fe has been applied to investigate structural properties of the axial ligands in ferric-high spin hematoheme-I, hematoheme-Te, and hematoheme-histidine-iodide. The magnitude and sign of the (129)I quadrupole coupling constant (e(2)qQ) and the isomer shift, as deduced from the Mossbauer effect spectra, are consistent with an axial, s-p hybridized bond of overwhelming sigma-character. Identical coupling constant (e(2)qQ((127)I) = -1826 +/- 3 MHz) were measured for both heme-I and hematoheme-histidine-iodide. Implications of this result to the nature of ferric-high spin heme-histidine complexing are discussed. A stable heme (125)Te species formed in the electron-capture decay of heme-(125)I is observed, and structural properties of this singly bonded telluride ligand are discussed.