Mossbauer Hyperfine Parameters Research Articles

Distribution of Fe<sup>3+</sup> in a synthetic (Ca,Na)<sub>2</sub>(Mg,Fe<sup>3+</sup>)Si<sub>2</sub>O<sub>7</sub>-melilite: <sup>57</sup>Fe Mössbauer and X-ray Rietveld studies

Crystal structure and the 57Fe Mossbauer spectrum of synthetic (Ca1.53Na0.47)(Mg0.52Fe3+0.49)Si1.99O7-melilite have been investigated to confirm the location of Fe3+ at the T1 site, and to evaluate the effect of an incommensurate structure on 57Fe Mossbauer hyperfine parameters. A conventional Rietveld refinement with occupancies of Ca(W), Na(W), Mg(T1), Fe3+(T1) and Si(T2) fixed to 0.765, 0.235, 0.515, 0.485 and 2.00, respectively, converged well with an Rwp (R-weighted pattern) of 13.14% and a goodness-of-fit of 1.337, indicating exclusive Fe3+ distribution at the T1 site. However, the Mossbauer spectrum consists of two doublets with an isomer shift of 0.19 mm/s and quadrupole splitting of 0.75 and 1.04 mm/s, which can be attributed to Fe3+ at the T1 site. There are two sorts of T1 site with distinguishable distortion in the synthetic Na-Fe3+-melilite, which might be attributed to the existence of an incommensurate phase at room temperature.

Hyperfine Interactions in Iron Meteorites: Comparative Study by Mössbauer Spectroscopy

The iron meteorites Sikhote—Alin, Bilibino, Chinga and Dronino with different Ni concentration and terrestrial age were studied by Mossbauer spectroscopy. Different Mossbauer hyperfine parameters were determined for studied meteorites and possible Fe-Ni phases were supposed.

Lithium insertion mechanism in CoSb3analysed by121Sb Mössbauer spectrometry, X-ray absorption spectroscopy and electronic structure calculations

The lithium insertion mechanism into the skutterudite-type CoSb3 compound has been studied using X-ray Absorption Near Edge Structure (XANES), 121Sb Mossbauer spectrometry and electronic structure calculations based on the Density Functional Theory (DFT) in the Linear Muffin Tin Orbital (LMTO) framework. 121Sb Mossbauer spectra are in agreement with a progressive restructuring which occurs during the second stage (voltage plateau at 0.6 V). The Mossbauer hyperfine parameters show the formation of Li3Sb and of a ternary intermediate phase LixCoSby whose variable composition depends on the insertion conditions. XANES spectra at Sb LI, III and Co K edges have been compared to calculated Projected Densities of States (PDOS) of reference compounds containing Co, Sb and Li. This analysis has allowed specification of the restructuring mechanism as a distortion of the CoSb6 octahedral units and confirms the formation of Li3Sb. The overall characterisations have been interpreted to suggest the first discharge mechanism of restructuring in accordance with the global reaction:CoSb3 + (y + z) Li → (LixCo1−mSby + m Co + Li3Sb) ↔ LizCo + y Li3Sb

Structural and Mössbauer spectroscopic study of hexagonal Laves-phase Zr(FexCr1−x)2 alloys and their hydrides

Abstract Hexagonal (C14) Laves-phase Zr(FexCr1−x)2 alloys with x=0.3, 0.4, 0.5, 0.6 and 0.7 have been prepared by arc melting and the corresponding hydrides have been formed by hydrogen uptake at 1 atm pressure. X-ray diffractograms have been measured and analyzed with the Rietveld method. 57Fe Mossbauer spectra, measured at room temperature, could be fitted with two doublets with 3:1 area ratio, corresponding to the two Fe sites in the C14 structure. The quadrupole splitting (Δ) and isomer shift (δ) dependences on x are discussed in terms of volume and charge effects. The hydrides showed volume expansions of up to 22% without any crystal structure change. Both Mossbauer hyperfine parameters Δ and δ increased markedly in the hydrides as compared to the alloys. Tetrahedral hole radii have been calculated from measured crystalline parameters and their relationship to hydrogen site preferences is discussed.

Electronic structure, spin couplings, and hyperfine properties of nanoscale molecular magnets

First-principles self-consistent spin-polarized electronic structure calculations were performed for the nanoscale magnetic molecules Mn12O12(CH3COO)16(H2O)4 and Fe11O6(OH)6(O2CPh)15 . The numerical Discrete Variational method was employed, within Density Functional theory. Charges and magnetic moments were obtained for the atoms, as well as Density of States diagrams, and charge and spin density maps. For Mn12O12(CH3COO)16(H2O)4 , values of the Heisenberg exchange parameters J were derived from the calculations; Mossbauer hyperfine parameters were calculated for Fe11O6(OH)6(O2CPh)15 and compared to reported experimental values. Key-words: Nanoscale; Molecular magnets.

First-principles calculations of Mössbauer hyperfine parameters for solids and large molecules

Electronic structure calculations based on density functional theory were performed for solids and large molecules. The solids were represented by clusters of 60–100 atoms embedded in the potential of the external crystal. Magnetic moments and Mossbauer hyperfine parameters were derived.

CEMS and AES Investigations on Iron Silicides

Thin layers of iron silicides produced by ion implantation were investigated by 57 Fe conversion electron Miissbauer spectroscopy and Auger electron spectroscopy. The Mossbauer hyperfine parameters were calculated and compared with results obtained at crystalline layers to determine the phases formed. It was found that, depending on the implantation conditions, the phases α- and β-FeSi 2 , e-FeSi or mixtures of them are formed. Auger electron spectroscopy was used to analyse the depth distribution of the elements in the layer. The iron concentrations necessary, according to the equilibrium phase diagram, to form the compounds mentioned above were not reached as a result of the implantation. Therefore, the formation of precipitates is concluded. Furthermore, it was found that the Si KLL Auger peak is very sensitive to silicide bonding. Its energy shift can be used as an indicator for silicide formation.

A crystallographic and mössbauer spectroscopy study of Fe2+3Al2Si3O12-Fe2+3Fe3+2Si3O12, (almandine-“skiagite”) and Ca3 Fe3+2Si3O12-Fe2+3Fe3+2Si3O12 (andradite-“skiagite”) garnet solid solutions

The crystal chemistry of garnet solid solutions on the Fe 3 2+ Al2Si3O12-Fe 3 2+ Fe 2 3+ Si3O12 (almandine-“skiagite”) and Ca3Fe 2 3+ Si3O12-Fe 3 2+ Fe 2 3+ Si3O12 (andradite-“skiagite”) joins have been investigated by single-crystal X-ray structure refinements and Mossbauer spectroscopy. Together, these two solid solution series encompass the complete range in Fe3+/ΣFe from 0.0 to 1.0. All garnets are isotropic and were re0fined in the Ia % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqaqFfpeea0xe9Lq-Jc9% qqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabG4mayaara% aaaa!3622! $$\bar 3$$ d space group. Small excess volumes of mixing are observed in andradite-“skiagite” solid solutions (W v =1.0±0.2 cm3 mol-1) and along the almandine-“skiagite” join (W v =-0.77±0.17cm3 mol-1). The octahedral (Al, Fe3+)-O bond lengths show a much greater variation across the almandine-skiagite join compared to the andradite-skiagite garnets. The dodecahedral (X)-O bond lengths show the opposite behaviour. In andradite-“skiagite” solid solutions, the octahedral site passes from being flattened to elongated parallel to the 3 axis of symmetry with increasing “skiagite” content. A perfect octahedron occurs in a composition of ≈35 mol% “skiagite”. The occupancy of the neighboring dodecahedral sites has the greatest effect on octahedral distortion and vice versa. The Mossbauer hyperfine parameters of Fe2+remain constant in both solid solutions. The hyperfine parameters of Fe3+ (at room temperature: centre shift=0.32–0.40 mm/sec, quadrupole splitting (QS)≈0.21–0.55 mm/ sec) indicate that all Fe3+ is in octahedral coordination. The Fe3+ parameters are nearly constant in almandine-“skiagite” solid solutions, but vary significantly across the andradite-“skiagite” join. The structural unit that contributes to the electric field gradient of the octahedral site is different from that of the coordinating oxygen polyhedron, probably involving the neighboring dodeca-hedral sites. Fe3+/ΣFe area ratios derived from the Mossbauer spectra systematically overestimate Fe3+ contents in both solid solutions series. This is attributable to different recoil-free fractions for Fe on the octahedral and dodecahedral sites. A correction has been derived that yields more accurate Fe3+/ΣFe ratios from room temperature and 80 K Mossbauer spectra.

Optical and m�ssbauer study of minerals of the eudialyte group

Twelve eudialyte specimens from the Khibini alkaline complex (Kola peninsula, USSR) have been studied by optical and Mossbauer spectroscopy methods. It has been found that in optically positive eudialytes Fe is mainly represented by Fe2+ ions in a rare planar four-fold coordination (Mossbauer hyperfine parameters — isomer shift IS=1.08 mm/s and quadrupole splitting QS=0.34 mm/s). It is these ions, not Mn3+ as it was assumed before, that are responsible for the crimson-red colour of eudialyte. In the optically negative red-brown and yellow-brown eudialytes (eucolites) Fe2+ ions are contained also in a tetragonal pyramid based on the above planar quadrangle (IS=1.33 mm/s and QS=2.24 mm/s). Major attention has been paid to an explanation of the colour and crystal-chemical features of optically positive in comparison with optically negative varieties of eudialytes.

Correlations between hyperfine parameters of Fe−Ni-B amorphous metals

The correlations between fluctuations in the57Fe Mossbauer hyperfine parameters of the amorphous alloys (Fe0.5Ni0.5)100−xBx (x=16, 18, 20, 22 and 25 at%) and FeyNi80−yB20 (y=20, 25, 40 and 60 at%) have been determined. Values of the correlation between the fluctuations of the isomer shift and the fluctuations of magnetic hyperfine field, μN 〈ΔHΔδ〉 together with published values on similar amorphous systems are compared with correlation values for related crystalline phases. The lack of characteristic values suggests that the correlation values do not allow a link to be made between local structural units in amorphous alloy and crystalline phases.

Mossbauer effect study of as-quenched, annealed and crystallised Fe95-xW5Bx metallic glasses

A 57Fe Mossbauer effect study of the as-quenched, annealed and crystallised Fe95-xW5Bx metallic glasses with x=15, 20 and 25 has been performed. For the as-quenched alloys, the fitting of the room-temperature Mossbauer spectra by the Window method yields the most probable and average hyperfine magnetic fields which appear to increase linearly with increasing boron concentration. The opposite trend observed in the variation of Mossbauer hyperfine parameters with temperature of annealing for the x=15 and 25 alloys at high annealing temperatures is due to changes taking place in the dense random packing structure of the alloys at the composition with x approximately=20. The Mossbauer studies of the crystallised Fe80W5B15 specimen show that the alloy undergoes a eutectic type of crystallisation. The different crystalline phases that emerge during the crystallisation of the present system are found to be alpha -Fe, Fe2B, (Fe0.8W0.2)3B and a nonmagnetic FeWB phase.

Mössbauer study of the quasi-binary sections FeSn2-FeSb2 and FeSn2-FeTe2 of the corresponding ternary systems Fe-Sn-Sb and Fe-Sn-Te

57Fe and119Sn Mossbauer and X-ray diffraction studies have been performed at room temperature to establish the presence of various intermediate phases in the quasibinary sections FeSn2-FeSb2 and FeSn2-FeTe2 {i.e. Fe (Sn1−xSbx)2 and Fe (Sn1−xTex)2 for 0≤x≤1·0 of the respective ternary systems Fe-Sn-Sb and Fe-Sn-Te at 500°C. Using significantly different Mossbauer hyperfine parameters and the X-ray powder diffraction patterns for each existing stable phase, solid solubility limits and presence of single and multiphase regions have been estimated and are reported.