Intensity of γ radiation back-scattered as a result of the Mössbauer effect

In the geometry of total backscattering, the intensity of scattered Mössbauer radiation is calculated. The contribution of various scattering channels to the spectrum is discussed: resonant and nonresonant, elastic and inelastic. Scattering at samples of different thickness is considered. Only one-time scattering of quanta in the material is taken into account.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii. Fizika, No. 8, pp. 23–29, August, 1989.     

57 Fe Mössbauer and X-ray characterisation of sandstones

Sandstones from the Free State province in South Africa have been mined and processed mainly by small scale and artisanal miners in the rural areas. In the present investigation basic fire proof and water absorption tests, X-ray and γ-ray based characterisation techniques were used to study the sandstones. The collected samples were grouped according to their apparent colour in day light conditions and the elemental analysis showed the presence of a high amount of oxygen (>52%) and silicon (>38%) with Mn, Al, Fe and Ca as major elements in proportions related to the colour distribution of the various sandstones. The uniaxial compressive stress was found to be the highest (56 MPa) for the greyish sandstone and the lowest (8 MPa) for the white sandstone sample, also associated with the lowest (Al+Fe)/Si value of 0.082. The humidity test showed that the 6 % water absorption was lower than the recommended ASTM value of 8 %. The sandstone samples were also subjected to various high temperatures to simulate possible fire conditions and it was found that the non alteration of the mineral species might be one of the reasons why the sandstones are regarded as the most refractory amongst the building materials typically used. Mössbauer spectroscopy revealed that iron is present in all the sandstones, mainly as Fe^3?+? with the black sandstone showing an additional presence of 3 % Fe^2?+? indicating that a higher iron content coupled to higher silicon content, contributes to an increase in the uniaxial compressive strength.     

193Ir and 57Fe Mössbauer characterisation of iridium/iron bimetallic catalysts for methanol synthesis

Fe-Ir/MgO catalysts derived from the [Et₄N]₂[Fe₂Ir₂(CO)₁₂] cluster precursor, which exhibit a high activity in the synthesis of methanol from CO and H₂, were studied by ¹⁹³Ir and ⁵⁷Fe Mössbauer spectroscopy. The study extends from the precursors via the fresh to the aged catalysts. The presence of iridium in the metallic state as well as the presence of trivalent, divalent and alloyed iron is detected. The different structural features of catalysts prepared from mixed-metal cluster compounds and from inorganic salt precursors are discussed.     

New applications of the Mössbauer effect

Results from a Mössbauer experiment to observe acoustic oscillations induced by pulsed laser excitation in MgO:⁵⁷Fe²⁺ crystal are presented. Time-domain spectra are satsifacorily described by the theory of the frequency modulation of Mössbauer radiation transmitted through a vibrating resonance medium. It is proposed that the D _4Ω/D _2Ω ratio of the fourth and second Fourier harmonics of the modulated radiation be used to measure the amplitude of nuclear oscillations.     

Size effect of Mössbauer parameters in iron oxide nanoparticles

The size dependence of Mössbauer parameters for iron oxide nanoparticles in the 10–25 nm range was investigated. It was shown that the isomer shift and hyperfine field parameters decrease with the nanoparticle size. Only at 25 nm the presence of magnetite was detected.     

Mössbauer effect studies of Fe–C combinatorially sputtered thin films

Alloys of Fe_{1? x} C _x were produced using combinatorial sputtering methods. The composition of the films as a function of position was determined using electron microprobe techniques and the results have shown that a composition range of about 0.35?<?x?<?0.75 was obtained. X-ray diffraction methods were employed to study the structure of the thin films and showed that all portions of the films were amorphous or nanostructured. Room temperature ⁵⁷Fe Mössbauer spectroscopy was utilized to study the atomic environment around the Fe atoms. Hyperfine field distributions of ferromagnetic alloys, as extracted from the Mössbauer analysis, suggested the existence of two classes of Fe sites: (1) classes of Fe sites that have primarily Fe neighbours corresponding to a high-field component in the distribution and (2) classes of Fe sites that have a greater number of C neighbours, corresponding to a low-field component. The magnetic splitting decreased as a function of increasing carbon concentration and alloys with x greater than about 0.68 were primarily paramagnetic in nature. These spectra exhibited distributions of quadrupole splitting with mean splitting in excess of 1.0?mm/s. This indicates a higher degree of local asymmetry around the Fe sites than typically seen in other Fe-metalloid systems.     

Mössbauer diagnostics of the isomorphic substitution of iron for aluminum in triclinic iron vanadate

Mössbauer spectroscopy and X-ray powder diffractometry (XRD) phase analysis are used to study mixed vanadates with the composition Al _x Fe_{3 ? x} V₃O₁₂, where x is 0, 0.3, 1.0, 1.5, 2.0, 2.7, and 3.0. Mössbauer spectroscopy is used to study the distribution of trivalent cations over different crystallographic positions. It is shown that the distribution of aluminum atoms differs from those expected from statistic and thermodynamic models.     

Mössbauer study of iron removal in a montmorillonite

⁵⁷Fe Mössbauer spectroscopy in conjunction with atomic absorption spectrometry and X-ray powder differaction analyses have been used to study the iron present in a montmorillonite prior to and after different successive stages of two deferration processes. Fe³⁺ ions occupy mainly octahedrical M(2) sites in the mineral structure; no impurities of iron oxides were detected. The quite efficient deferration by HCl refluxing produced a substantial alteration of lamellar structure of montmorillonite, whilst dithionite/citrate treatment did not induce severe structural changes but had low iron removal efficiency.     

Mössbauer effect study of iron decahydrodecaborate chelates containing ferrocenyl group

⁵⁷Fe Mössbauer parameters of three chelates containing ferrocenyl group have been extracted over a temperature range from 12 K to 300 K. In comparison with ferrocene itself it is found that the substituents attached to the cyclopentadienyl ring by -bonding can give an appreciable effect on bonding of central iron atom.Work supported by the Chinese National Science Foundation.     

Mössbauer effect and X-ray diffraction investigation of Si–Fe thin films

An X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy investigation of Si_{100– x} Fe _x (0?<?x?<?80) thin films prepared by combinatorial sputtering methods is reported. Resulting Mössbauer spectra were fit to Voigt-based distributions of quadrupole doublets for paramagnetic spectral components and Zeeman split sextets for ferromagnetic spectral components. In conjunction with the X-ray measurements, these results show that the Si-rich films are a mixture of dilute Fe in amorphous Si and an approximately equiatomic amorphous SiFe phase. Fe-rich films show the presence of a ferromagnetically ordered phase. For x?<?73, this ferromagnetic phase is amorphous or nanostructured and for x?≥?73, the phase is shown to be a crystalline bcc phase. Results are discussed in terms of short-range structural ordering in these alloys.     

Mössbauer spectroscopy of Al substituted Fe in holmium iron garnet

A Mössbauer spectroscopy study was made on Ho₃Fe_5-xAl_xO₁₂ (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (B_hf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with B_hf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in B_hf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.     

Use of Mössbauer effect for ion-exchange resins investigation

Results of gamma-resonance spectroscopy investigation of iron ions sorption by aminocarboxylic ampholytes ANKB-2 and ANKB-50 are presented. Conclusions on the forms of the complexes produced in the phase of hydrated ion-exchangers are drawn.     

Mössbauer studies of iron stabilised polymethacrylates

Polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA) and polybutyl methacrylate (PBuMA) containing ferric chloride and ferrous sulphate as stabilisers, were prepared by free radical polymerization. Mössbauer spactra of ferrous sulphate stabilised polymers don't show any change in the value of isomer shift (1.30 mm/s) while quadrupole splitting values are quite different from those for pure ferrous sulphate. This indicates that environment of Fe²⁺ moiety changes in polymers and thus stabilises the polymers. In case of ferric chloride stabilised polymers the isomer shift values don't differ significantly for different polymethacrylates but quadrupole splitting values increase from polymethyl methacrylate to polybutyl methacrylate. The TGA analysis shows that the inclusion of iron salts stabilises the polymers by 40°C (approx.) and at higher temperatures α-Fe₂O₃ is formed.     

Mössbauer effect studies of the Dy12Fe82B6 system

The Mössbauer measurements of both⁵⁷Fe and¹⁶¹Dy in Dy₁₂Fe₈₂B₆ system are reported. The presence of B exceeds the magnetic hyperfine fields at both⁵⁷Fe and¹⁶¹Dy nuclei as compared to corresponding pure metals Fe and Dy respectively. The only small excess of the hyperfine field at⁵⁷Fe nucleus is observed. The excess at¹⁶¹Dy nucleus is about 12% of the free ion Dy³⁺ value.     

Application of Mössbauer spectroscopy for the complex structural analysis of iron oxide-based nanomaterials

The results of complex structural investigation by XRD, TEM, and Mössbauer spectroscopy of nanomaterials based on iron oxides Fe₃O₄ and γ-Fe₂O₃ are presented. The investigated nanomaterials include nanopowders produced chemically and nanostructural powders produced mechanochemically. The magnetic properties of the nanomaterials, measured at ambient temperature, are discussed.     

Mössbauer effect diffraction from polycrystalline57Fe

We built a Debye-Scherrer type powder diffractometer with a⁵⁷Co radiation source and a large-angle position-sensitive detector. We tuned the incident -ray beam on and off the Mössbauer effect resonance, and measured diffraction patterns from our textured samples of polycrystalline⁵⁷Fe. Mössbauer effect diffraction dominated over X-ray diffraction for the higher order Bragg peaks.     

The influence of pressure on the Mössbauer effect

A study was made of the pressure dependence of the intensity of the Mössbauer line, and the dependence of this quantity on the specific volume of the crystal, which has the same form for all these crystals in the first approximation, was derived for regular atomic crystals in the Grüneisen approximation. The change in intensity of the Mössbauer line due to pressure can be converted, except for a multiplication factor, to a change in intensity of this line caused by a change in temperature.     

Will the iron age of superconductivity become the Mössbauer age?

The discovery of new iron-containing high-temperature superconductors is considered in relation to their studies by means of the Mössbauer effect. The importance of the relevant results for the problem of the coexistence of magnetism and superconductivity and the stability of superconductivity against to disorder is shown by analyzing the available literature data.