Mössbauer study of Fe-Re alloys prepared by mechanical alloying

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for nanocrystalline iron-based solid solutions Fe _1?x Re _x , prepared by mechanical alloying with x in the range 0.01 ≤ x ≤ 0.04. The obtained data were analysed in terms of the binding energy E _b between two rhenium atoms in the Fe-Re system. The extrapolated value of E _b for x = 0 was used for computation of enthalpy of solution of rhenium in iron. The result was compared with that resulting from the cellular atomic model of alloys by Miedema as well as with value, derived from proper data for Fe-Re solid solutions obtained by melting in an arc furnace. From the comparison it follows that our findings are in agreement with the Miedema’s model predictions and previous Mössbauer studies.     

Mössbauer study of CO-precipitated Fischer-Tropsch iron catalysts

Mössbauer spectroscopy studies of precipitated Fischer-Tropsch (FT) iron catalysts, viz. 100 Fe/5 Cu/4.2 K/x SiO₂, wherex=0,8, 16, 24, 25, 40, or 100, have shown that reduction of the oxide precursor in CO gives rise to -carbide Fe₅C₂ whose amount decreases with an increase of SiO₂ content. The -carbide is converted into magnetite Fe₃O₄ while catalyzing the FT synthesis reaction. A correlation between FT activity and the content of -carbide in the catalysts was found, which indicated that -carbide is active for FT synthesis reaction.     

Mössbauer study of carbon-supported α-Fe catalysts

Mössbauer spectra of carefully reduced carbon-supported iron catalysts show superparamagnetic -Fe at 80 K. The results indicate that the particle size depends on the reduction temperature. Effects of evacuation and CO chemisorption are discussed.     

Mössbauer study of supported Pt—Sn

Pt—Sn supported on alumina was characterized before and after treatment with hydrogen by Mössbauer spectroscopy and X-ray diffraction. For the calcined sample tin is present as SnO₂ and platinum as metal. After reduction with hydrogen, Sn(IV), Sn(II), Sn(0), Pt, Pt₃Sn, PtSn alloys are formed. SnO interacts strongly with the support.     

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.     

Mössbauer study of FINEMET with different permeability

Stress field and magnetic field annealed FINEMET ribbons were investigated by ⁵⁷Fe Mössbauer spectroscopy, magnetic and XRD methods. The change in relative areas of the 2nd and 5th lines in the Mössbauer spectra indicated significant variation in magnetic anisotropy due to the different annealing. High velocity resolution Mössbauer spectroscopy was also used to control the model applied for the evaluation of Mössbauer spectra. A correlation was found between the permeability and the magnetic anisotropy of the annealed FINEMET samples. This can be applied to predict production parameters of FINEMET ribbons with more favorable soft magnetic properties for technological applications.     

Crystal structure and Mössbauer spectroscopic study of FeSnF6·6H2O

Large single crystals of FeSnF₆·6H₂O were grown when aqueous hydrofluoric solutions of SnF₂ and FeF₂ were allowed to evaporate in air. Tin-119 Mössbauer spectroscopy at ambient temperature shows a single line at slightly negative isomer shift relative to CaSnO₃ at room temperature (=–0.380(6) mm/s, =0). This is characteristic of tetravalent tin octahedrally coordinated by fluorine. The X-ray crystal structure shows that tin(IV) is coordinated by 6 fluorine atoms, and Fe(II) by 6 water molecules. Both sites show a slight distortion from octahedral symmetry: the six distances are equal (Sn-Fe=1.941(3) Å and Fe-O=2.112(3) Å), whereas there are two values of angles (Fe-Sn-F=90.4(1)° and 89.6(1)°; O-Fe-O=91.1(1)° and 88.9(1)°). The material is an ionic compound [SnF₆]^2–[Fe(H₂O)₆]²⁺.     

A Mössbauer effect study of MgFe2O4

A slowly cooled sample of the ferrimagnetic spinel MgFe₂O₄ has been studied with ⁵⁷Fe Mössbauer spectroscopy over a wide temperature range both with and without high magnetic fields. The observed temperature dependence of the A and B site hyperfine parameters is discussed. Conclusions about the spin structure, the magnetic exchange interactions and the supertransferred hyperfine fields are presented.     

Mössbauer effect study of Ni1−xCuxMnyFe2−yO4 system

The Mössbauer effect technique has been employed for the study of magnetic properties of spinel series Ni_1?xCu_xMn_yFe_2?yO₄ with 0.0≤x≤1.0, and y=0.6. The substitution of Mn³⁺ and Cu²⁺ ions results in a slight decrease of the hyperfine field at B‐ as well as A‐sites. The area ratio of Fe³⁺ ions at the A‐ and B‐site at 77 K indicates that Cu²⁺, Ni²⁺ and Mn³⁺ ions occupy the octahedral sites in an evidence for complete inverse spinel in this system. The temperature dependence of the hyperfine parameters has been studied for composition with x=0.5 where Nèel point T_N and Debye temperature θ_D are found to be 650 and 679 K, respectively. The temperature dependence of the sublattice magnetization σ(T) obeys a one‐third‐power law in the range 0.5N<0.99.     

Mössbauer study of mixed valent silicides Eu(Ir1−x Pd x )2Si2

The solid solutions Eu(Ir_1–x Pd _x )₂Si₂, which exist for 0x0.125 and 0.75x1. cristallize with the tetragonal ThCr₂Si₂-type structure. The variation of the europium valence with composition has been thoroughly studied at temperatures 4.2T293 K by¹⁵¹Eu Mössbauer resonance. For 0x0.125 the europium valence at room temperature decreases asx increases. For 0.75x1 the valence transition temperature Eu³⁺Eu²⁺ increases asx increases.     

A Mössbauer spectroscopic study of cobalt-iron molybdates

Fe _x Co_1–x MoO₄ compounds prepared by coprecipitation were studied by XRD, electrical conductivity and mainly by absorption and emission Mössbauer spectroscopy. FeMoO₄ and CoMoO₄ samples were shown to contain Fe³⁺ and Co³⁺, respectively, in solid solution. Three kinds of Fe _x Co_1–x MoO₄ solids can be described. Forx0.16: one has a -Co(Fe²⁺, Fe³⁺)MoO₄ solid solution. For 0.17x0.25: one has the same solid solution with its surface rich in Fe³⁺. Forx0.26: one has the same solid solution with only bulk Fe³⁺, and ferric molybdate. Studies of reduction by hydrogen and of catalytic reaction of mechanical mixtures of CoMoO₄ and ferric molybdate support these statements.     

A Mössbauer study of some new trinuclear Fe−S cluster compounds

The reaction of (u-RS)₂ (XMgS) Fe₂ (CO)₂ with CpFe (CO)₂I gave thirteen new compounds (u-RS) [CpFe (CO)₂S] Fe₂ (CO)₄. Mossbauer spectra were obtained at 80K. Two quadrupote doubles (A set and B set) were present. The ratio of areas between A set and B set was close to 21. The molecule of every compound contained two Fe (2+) which were in the same chemical environment of low spin state with a coordination number of six, and the Mossbauer parameters of the two Fe (2+), IS=0.2–0.3 mm/s, QS=0.7–0.8 mm/s. In addition, the molecule contained a Fe (3+) in low spin state which was proved by ESR. Its Mossbauer parameters, IS=0.4–0.5 mm/s. QS=1.5±1.6 mm/s, The molecular structure of (u-MeS) [u-CpFe (CO)₂S] Fe₂ (CO)₄ was determined by X-ray diffraction, monoclinic form, space group P21/n z=4, unit cell parameters, a=7.90A, b=10.77A, c=22.53A.     

Magnetic Properties of Np2Ir2In Investigated by 237Np Mössbauer Spectroscopy

The present study of Np₂Ir₂In completes the ²³⁷Np Mössbauer spectroscopy investigations of Np₂T₂X (T = Co, Rh, Ir, Ni, Pd, Pt; X = In, Sn) compounds. Np₂Ir₂In is found to order at T _ord30 K and the complex Mössbauer spectra suggest the occurrence of a noncollinear modulated magnetic structure with an average magnetic moment on the neptunium _Np0.76 _B. The magnetic properties of Np₂Ir₂In are consistent with the general trends observed in the An₂T₂X (An =U, Np) isostructural family.     

Mössbauer study of Cu1−xZnxFe2O4 catalytic materials

In the present work, we have synthesized and characterized magnetic nanoparticles of maghemite γ-Fe₂O₃ to study their structural and magnetic properties. For the preparation, magnetite precursor, were oxidized by adjusting the pH = 3.5 at about 80 °C in an acid medium, The mean size of the maghemite particles calculated from the X-ray diffractogram was around 5.7 nm. Mössbauer spectroscopy measurements at room temperature show their superparamagnetic behavior. Furhermore, Mössbauer measurements were carried out at 77 K and 4.2 K in order to find the typical hyperfine fields of the maghemite. Magnetite phase was not found. FC and ZFC magnetization curves measured at 500 Oe indicate a blocking temperature of 105.3 K. The magnetization measurements also show almost zero coercivity at RT. TEM images show nanoparticles with diameter smaller than 10 nm, which are in good agreement with the X-ray pattern and the fitting of the magnetization data.     

Mössbauer study of Hungarian phlogopites

Ultramafic xenoliths of mantle origin occur in Hungarian Cretaceous lamprophyres. The aim of the present work was to determine the iron positions and their occupancy in phlogopites originated from ultramafic xenoliths by the help of Mössbauer spectroscopy. On the basis of the evaluation of the Mössbauer spectra Fe _M1 ²⁺ , Fe _M2 ²⁺ , Fe _M2 ³⁺ and Fe _M1 ³⁺ (or in some cases Fe_tet) octahedral and tetrahedral iron sites were identified in the samples. Quantitative analysis was performed for all of the iron sites. We have observed large differences between the Fe²⁺/Fe³⁺ ratio in samples originated from 120–150 km deepness, which phlogopites having been existed at different erosion circumstances. We have found a significantly higher Fe²⁺/Fe³⁺ ratio in phlogopites which had been solidified in 120–150 km depth from the surface of Earth 70–100 million years ago, than those had been crystallized in 60–80 km deepness.     

Mössbauer study of Slovak meteorites

⁵⁷Fe Mössbauer spectroscopy was used as an analytical tool in the investigation of iron containing compounds of two meteorites (Rumanová and Ko?ice) out of total of six which had fallen on Slovak territory. In the magnetic fraction of the iron bearing compounds in the Rumanová meteorite, maghemite, troilite and Fe-Ni alloy were identified. In the non-magnetic fraction silicate phases were found, such as olivine and pyroxene. The paramagnetic component containing Fe^3?+? ions corresponds probably to small superparamagnetic particles. The Ko?ice meteorite was found near the town of Ko?ice in February 2010. Its magnetic fraction consists of a Fe-Ni alloy with the Mössbauer parameters of the magnetic field corresponding to kamacite α-Fe(Ni, Co) and troilite. The non-magnetic part consists of Fe^2?+? phases such as olivine and pyroxene and traces of a Fe^3?+? phase. The main difference between these meteorites is their iron oxide content. These kinds of analyses can bring important knowledge about phases and compounds formed in extraterrestrial conditions, which have other features than their terrestrial analogues.     

Mössbauer study of natural wolframites

Natural Wolframite, (Fe _x Mn_1?x )WO₄ withx=0.95 to 0.41, obtained from seven different sites of two quartz-wolframites deposits of Degana and Sirohi in Rajasthan. India, have been studied by Mössbauer spectroscopy down to 20 K. X-ray diffraction studies with a monochromatic Cu radiation (λK_a-1.5405 Å), were carried out to determine the value ofx. The Mössbauer spectra of all seven samples were recored at 300, 200, 100, 50, 40, 30 and 20 K, and were least square fitted for different sites. The Mössbauer parameters are attributed to a high spin ferrous ion in a quite distorted octahedral symmetry, and only one sextet has been resolved below transition temperature.