Determination of quadrupole splitting for 57Fe in M1 and M2 sites of both olivine and pyroxene in ordinary chondrites using Mössbauer spectroscopy with high velocity resolution

Study of 11 ordinary chondrites using Mössbauer spectroscopy with high velocity resolution revealed two crystallographically non-equivalent octahedral sites M1 and M2 in subspectra of olivine and pyroxene which were observed previously in pure natural or synthetic silicates only. Mössbauer hyperfine parameters related to M1 and M2 sites in olivine and pyroxene determined from Mössbauer spectra of ordinary chondrites were analyzed and compared with parameters of pure natural and synthetic silicates.     

Crystal-field interpretation of the temperature dependence of the57Fe Mössbauer quadrupole splitting in two orthopyroxenes

The temperature dependences of the M2 and the M1 ferrous quadrupole splittings in two orthopyroxenes have been studied. The valence contributions to the EFG were calculated from the Boltzmann averages of the expectation values of the EFG components over the corresponding⁵D levels, while the lattice contributions were obtained from lattice summations. The proper⁵D level schemes were each determined by diagonalization of the full crystal-field Hamiltonian, for which the operator coefficients were calculated so as to take into account the real C₁ symmetry of the FeO ₆ ^10– clusters. The calculations were based on the lattice and the charge data related to ferrosilite.     

The quadrupole interaction of57Fe in Ti

The quadrupole interaction of⁵⁷Fe in titanium was studied by Mössbauer spectroscopy and by the time-differential perturted angular correlation technique, using an implanted and diffused source of⁵⁷Co in titanium. From the latter measurements a quadrupole interaction frequencyv _Q = 2.22 ± 0.42 MHz was derived. The modulation amplitude of the delayed coincidence spectrum combined with the Mössbauer spectra indicate a high degree of substitutionality of the cobalt in the titanium.     

Ab initio study of the 57Fe quadrupole splitting in the heme models of α- and β-subunits in tetrameric deoxyhemoglobin

Ab initio Xα discrete variation method was used for calculation of quadrupole splitting for the rough heme models in α- and β-subunits of tetrameric deoxyhemoglobin accounting small stereochemical variations. The differences of theoretical values of quadrupole splitting for these heme models were obtained.     

Mössbauer study of Fe57 and Co57 in Co1 + xV2−xO4

Mössbauer sources and absorbers, prepared by doping Fe⁵⁷ and radioactive Co⁵⁷ into samples of Co_1?xV_2?xO₄ (0 ? x ? 1), were studied in the temperature range of 80–500 K. The source and absorber spectra are very similar. The absence of any Fe²⁺ at the A site can be understood by partial covalent bond formation with an anion. However, the predominance of Fe³⁺ at the B site (with some Fe²⁺ for x = 1) cannot be explained by simple crystal-field or molecular-orbital theories. The x dependence of the isomer shift and of the Fe³⁺B-site quadrupole interaction can be related to changes in the lattice constant and the oxygen parameter. The temperature dependence of the Fe²⁺B-site quadrupole interaction can be fitted in the motional-averaging model. In the range of 0 ? x ? 0.5 the temperature dependence of the isomer shift shows effects of chemical bonding beyond the second-order Doppler shift.     

Determination of the quadrupole splitting distributions of the A- and B-site ferrous ions in Fe2TiO4

Fe₂TiO₄ has been investigated using⁵⁷Fe Mössbauer spectroscopy with the aim of determining the shape and the temperature dependence of the separate A- and B-site quadrupole splitting distributions. This has been impossible hereto because both contributions are strongly overlapping and the normal doublet spectra do not contain enough information to differentiate between both. It is found that, through th use of external magnetic fields, the necessary information to perform the separation is unveiled. Furthermore, the change in shape as a function of temperature of the distributions thus obtained is well understood from the known behaviour of Fe²⁺.     

57Fe Mössbauer studies of U(Fe1−x Co x )2

In the pseudo-binary alloy system U(Fe_1–x Co_x)₂, the ordering transition temperature and the magnetic moment decrease rapidly with x.⁵⁷Fe Mössbauer measurements on the alloys (x=0.08 and 0.20) have been performed as a function of temperature. The observed hyperfine field at the⁵⁷Fe nucleus is much reduced with respect to that in UFe₂.     

A Mössbauer investigation of the quadrupole splitting in β-FeOOH

High resolution ⁵⁷Fe Mössbauer effect measurements at room temperature show that the spectra of pure, synthetic β-FeOOH in its paramagnetic state consist of a superposition of two discrete doublets, due to the existence of two different electric field gradients (EFG) which are proven to be related to the presence of halogen ions in this compound.     

Fe57 Mössbauer effect study of the metallic glasses Y1−xFex2

The compositional variation of atomic density and Fe⁵⁷ Mössbauer Effect spectra in the paramagnetic metallic glasses Y_1?xFe_x has been investigated. The spectra consist of two fairly well defined symmetric lines for all compositions studied (0.25 ? x ? 0.45). A sensitive compositional dependence has been observed for the quadrupole splitting, isomer shift, and to a lesser extent the atomic density. This behavior disagrees with the predictions of models based on random packing of hard spheres. Explanations based on enhanced chemical ordering and a tendency towards phase separation are discussed.     

A study of57Fe Mössbauer effect in Nd2Fe14C

Combining ME and NMR investigations of Nd₂Fe₁₄C compound, the hyperfine field values at 4.2 K and their assignment to the six Fe sites have been determined to be in following sequence: 26.8 (4e), 29.8 (4c), 30.9 (16k₁), 31.6 (8j₁), 33.9 (16k₂), 36.9(8j₂) Tesla(T). The Mössbauer measurements of the sample were carried out between 4.2 K and 300 K. It was found that a spin reorientation takes place at about 140–150 K and the canting angle is about 29.     

Mössbauer studie of Co2B by doping 1 at %57Fe

In order to clarify the direction of the easy axis of Co₂B, we examined Co₂B doped with 1 at %⁵⁷Fe using Mössbauer spectroscopy. In the temperature range 4.2 K≤T≤r.t., two well resolved six-line patterns having equal intensity were observed. This shows that the easy axis lies in the c plane. The displacement of magnetically split absorption lines by quadrupole interaction also supports this conclusion. In the temperature region between 4.2 K and 1.6 K, the direction of the easy axis seems to begin to deviate from the c plane.     

Nuclear quadrupole moment of 57Fe from microscopic nuclear and atomic calculations

The nuclear quadrupole moment (NQM) of the Ipi = 3/2(-) excited nuclear state of 57Fe at 14.41 keV, important in M?ssbauer spectroscopy, is determined from the large-scale nuclear shell-model calculations for 54Fe, 57Fe, and also from the electronic ab initio and density functional theory calculations including solid state and electron correlation effects for the molecules Fe(CO)(5) and Fe(C5H5)(2). Both independent methods yield very similar results. The recommended value is 0.15(2) e b. The NQM of the isomeric 10+ in 54Fe has also been calculated. The new NQM values for 54Fe and 57Fe are consistent with the perturbed angular distribution data.     

Mössbauer study on M1 and M2 sites of Fe2+ in natural hypersthene under dynamic crystal field potential approach

⁵⁷Fe Mössbauer spectra of hypersthene, a natural silicate mineral belonging to the orthopyroxene group, have been taken over the temperature range 77–292 K. At temperatures above 77 K, they show asymmetric quadrupole peaks. This asymmetry arises from the overlapping of two quadrupole doublets from Fe²⁺(3d⁶,⁵D) ions in two different sites (M1 and M2). The quadrupole splitting, isomer shift and their temperature dependence are appreciably different for Fe²⁺ ions in the two sites. The Fe²⁺ quadrupole splitting in the M1 site decreases linearly with temperature, which can be explained quite satisfactorily by using a very simple model of the orbit-lattice interaction.     

57Mössbauer studies in the double transition Ce(Fe1−xCox)2 alloys

The reported double transition in the series Ce(Fe_1–xCo_x)₂ for x<0.3 has been shown to be due to spin reorientation from Mossbauer measurements at⁵⁷Fe. It is suggested that the competing interactions with randomly substitution of Fe by Co atoms causes a quasi random freezing which results in abrupt loss of magnetization.     

Trends in Mössbauer emission spectroscopy of57Co/57Fe

⁵⁷Co Mössbauer emission spectroscopy is briefly reviewed summarizing mainly the results of the last three to four years. Special emphasis is given to topics easily accessible to groups just starting their activity in this field. On the basis of the trends, the most interesting topics of the upcoming years are estimated.     

Atomic short-range order in Fe1−xCrx alloys studied by 57Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for iron-based solid solutions Fe_1?xCr_x with x in the range of 0.01≤x≤0.10. Analysis of the obtained spectra gave clear evidence that the distribution of impurity atoms in the first coordination spheres of ⁵⁷Fe nuclei is not homogeneous and it cannot be described in terms of binomial distribution. Quantitatively, the effects were described in terms of the short-range order parameters.