Mössbauer effect and XRD studies of iron-zinc binary alloys

Mössbauer spectroscopy and XRD were employed to characterize the microstructural properties of iron-zinc binary alloys between 0–31 at.% Fe. Samples were prepared with accuracies of ±0.5 at.% Fe, and the Mössbauer and lattice parameters were monitored as a function of iron concentration across each phase. Two iron sites were observed in the phase (18–31 at.% Fe), whose occupancies and isomer shifts varied continuously with iron content. However, the quadrupole splitting of each site remained constant. Within the ₁ phase (19–24 at.% Fe), three iron sites were observed whose isomer shifts and quadrupole splittings remained constant, while their occupancies varied with iron concentration. For the first time, a third iron site was observed in the phase (8–13 at.% Fe), whose occupancy increases with iron content. Also, the site occupancies of the two other sites appear to remain constant, while other Mössbauer parameters vary continuously with iron content. Analysis of the phase (6–7 at.% Fe) showed the presence of one iron site, whose parameters were not observed to change due to the small variance in iron concentration. XRD studies indicate the lattice parameters across the and phases vary continuously with iron concentration. Moreover, a better understanding of these phases, as formed in galvanneal steel coatings, was obtained.Research supported by the International Lead Zinc Research Organization, Inc., Grant No. ZM-403 and Virginia's Center for Innovative Technology, Grant No. MAT-92-007-01.     

Mössbauer spectroscopy of zirconium alloys

Mössbauer investigations of zirconium alloys were examined. Data about the chemical state of iron atoms in the zirconium alloys of different composition has been provided. Mössbauer spectroscopy revealed that small quantities of iron in binary zirconium alloy are in the solid solution α-Zr (up to 0.02 wt.%). Different iron atoms concentration and thermo-mechanical treatments may lead to formation the intermetallic compounds Zr₃Fe, Zr₂Fe, ZrFe₂. Adding tin atoms does not affect the formation and shape of Mössbauer spectra of these compounds. Adding Cr and Nb atoms makes significant changes in the shape of Mössbauer spectra and leads to the formation of complex intermetallic compounds. Adding Cu and W atoms, the shape of the binary alloys spectra (Zr-Fe) remains unchanged, but a change in the temperature dependence behavior of the spectral parameters occurs and also, changes to the properties of the alloys.     

Surface and bulk Mössbauer effect studies of annealed NANOPERM-type alloys

Structure, hyperfine interactions, and magnetic behaviour of Fe₈₀M₇Cu₁B₁₂ (M=Mo, Nb, Ti) nanocrystalline alloys are studied by Mössbauer spectrometry. As-quenched and heat-treated specimens are investigated. Transmission and Conversion Electron Mössbauer effect techniques are used to compare surface and bulk crystallization as a function of annealing temperature with the aim to unveil the crystallization onset. In addition, magnetic structure comprising distributions of hyperfine fields is discussed as a function of composition and annealing temperature. Hyperfine field distributions are obtained separately for the amorphous residual phase and for interface regions. Crystalline phases are represented by discrete components.     

Mössbauer studies of subfossil oak

With the PANDA experiment at the FAIR facility in Darmstadt, Germany it will be possible to investigate antiproton-nucleus reactions in an energy range not explored so far. This provides opportunities for unique measurements of which some are outlined in this article. Possible modifications of hadron properties in nuclear matter is subject of extensive theoretical and experimental studies. With PANDA it will be possible to extend this kind of studies to the charm sector. A study of particular interest will be to measure the J/Ψ-nucleon dissociation cross-section. This cross-section is relevant for the interpretation of the J/Ψ suppression observed in high energy heavy ion reactions. Further topics include the study of antibaryons in nuclei and short-range nucleon-nucleon correlations.     

Critical behaviour of Ho 2 Fe 17 − x Mn x —magnetisation and Mössbauer spectroscopy

The magnetic properties of Ho₂Fe_17???xMn_x compounds (x = 0–2) of ferromagnetic ordering temperatures up to T_C ~344 K have been investigated by DC magnetization and Mössbauer effect measurements. The nature of the magnetic phase transitions and the critical behaviour around T_C has been investigated by analysis of the magnetisation data and the critical exponents β, γ and δ determined. The critical exponents are found to be similar to the theoretical values of the mean-field model for which β?=?0.5 and γ?=?1.0, indicating the existence of a long-range ferromagnetic interactions. The isothermal entropy changes ΔS around T_C have been determined as a function of temperature in different magnetic fields.     

57Fe Mössbauer study of sol–gel synthesized Sn1 − x − y Fe x Sb y O2 − δ powders

Samples of SnO₂ doped with different amount of Fe (10–20%) and Sb (5–25%) were prepared by sol–gel method. Room temperature ferromagnetism was found to increase as a result of co-doping with Sb, as compared to SnO₂ doped only with Fe. ⁵⁷Fe Mössbauer spectra of almost all samples exhibited two paramagnetic doublets and a small subspectrum referring to magnetic relaxation at room temperature. Only the samples Sn_0.65Fe_0.2Sb_0.15O_2???δ and Sn_0.85Fe_0.1Sb_0.05O_2???δ with 4 h long annealing time showed well developed sextets and larger magnetic coercivity compared to that of the other samples. The sextet observed was considered to be due to precipitates like Sn doped α-Fe₂O₃. The results suggest that the origin of the magnetic interactions is enhanced by the presence of magnetic defects, which can interact with the iron ions by free carrier electrons. For the sample with precipitates, the grain boundary defects may play an important role of enhanced ferromagnetism.     

Mössbauer studies of Fe x Mn1 − x S single crystals

Single crystals of iron manganese sulfides Fe _x Mn_{1 ? x} S (0.25 ≤ x ≤ 0.29) are experimentally investigated using Mössbauer spectroscopy and x-ray diffraction. The Mössbauer spectra measured at 300 K exhibit a single broadened line characteristic of paramagnets. The isomer shift of this line is equal to 0.92–0.94 mm/s, which is typical of Fe²⁺ ions in the octahedral position. The quadrupole splitting (0.18–0.21 mm/s) suggests a distortion of the coordination polyhedron of iron ions in the Fe _x Mn_{1 ? x} S compounds.     

Mössbauer studies of selected synthetic silicates

Mössbauer spectra of fayalite-, 7#x03B1;-Fe₂SiO₄, powder and single crystals were taken in the antiferromagnetic temperature region below T _N?65 K. The orientation of the efg and H(0) with respect to the crystallographic axes was determined as function of the temperature and compared to neutron diffraction and magnetic susceptibility data. A similar study was performed with Li‐acmite LiFeSi₂O₆, whose magnetic structure can be regarded as a model compound for quasi one‐dimensional systems. Synthetic annite KFe₃[AlSi₃O₁₀(OH)₂] has to contain at least about 10% Fe³⁺ in order to be stable. A comparison of the evaluation of the spectra assuming either Lorentzian line shape of the doublets or quadrupole splitting distributions QSDs shows that Fe³⁺/Fe²⁺‐ratios can be determined precisely by both methods. However, M2/M1-site distributions cannot be evaluated with great accuracy. In ilvaite CaFe₃[Si₂O₇/O/(OH)], there is a thermally activated intersite electron hopping between Fe²⁺ and Fe³⁺ at temperatures around 300 K in a double octahedron chain. At temperatures above 395 K there is extended electron delocalization in a narrow d‐ or polaron‐band. The substitution of Fe by Mn favours both effects and lowers the temperature of the crystallographic phase transition monoclinic to orthorhombic distinctly. In the solid solution series member acmite(50%)‐hedenbergite(50%) Na_0.5Ca_0.5Fe₂[Si₂O₆] just intersite electron hopping between Fe²⁺ and Fe³⁺ in the M1 octahedron chain and no formation of polaron bands is observed. This is explained by the larger Fe–Fe‐intrachain distances compared to those in ilvaite or magnetite.     

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 studies of baotite and bafertisite

The Mössbauer effect was used to study silicate minerals of baotite and bafertisite at 298 K and 95 K. Each spectrum of baotite at 298 K and 95 K consists of two doublets, and they are contributed from Fe²⁺ and Fe³⁺ in the octahedral Tisites, respectively. Each spectrum of bafertisite at 298 K and 95 K is composed of two doublets, and they are mainly caused by Fe²⁺ in the octahedral Fe(I) and Fe(II)sites, respectively. The average effective ionic radii of the Ti sites in baotite and the Fe(I) and Fe(II)sites in bafertisite were estimated based on the correlation of the isomer shifts with the average effective ionic radii in silicates, and they are 0.56 , 0.73 and 0.73 , respectively.     

Mössbauer studies of Al75Cu15−xFexV10 icosahedral alloys

⁵⁷Fe Mössbauer effect measurements have been performed at room temperature on the alloy series Al₇₅Cu_15–xFe_xV₁₀ withx=0.15 (amorphous and icosahedral phases), 3 and 6 (icosahedral phases). There is more disorder in the icosahedral phase of thex=0.15 alloy than in its amorphous phase. The bimodal character of the distribution of quadrupole splittings becomes less pronounced with increasingx and disappears forx6. This is interpreted in terms of two classes of transition metal sites in Al-transition metal-based icosahedral alloys.     

Structural and Mössbauer spectroscopic studies of Fe0.7−xCrxAl0.3 alloys

Fe_0.7−xCr_xAl_0.3 alloys with x=0, 0.1, 0.2, 0.3 and 0.35 have been synthesized by arc melting and studied by X-ray diffraction and Mössbauer spectroscopy. All the samples studied were found to have single phase with body center cubic structure. The lattice parameter a, and hence the volume, were obtained from the X-ray diffraction patern and found to increase with increasing the chromium concentration. At room temperature Mössbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x under investigation. The Mössbauer spectra were analyzed considering a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x. During the fitting procedure, the relation between the hyperfine field and the isomer shift in the hyperfine field distribution was linear relation. The average hyperfine field and isomer shift as a function of chromium content x were found to decrease with increasing x. The results are explained in terms of local environmental effects on the hyperfine interactions.     

Tin Mössbauer spectroscopy of tin-rich iridium-tin alloys

Ir₅Sn₇, Ir₃Sn₇ and newly obtained IrSn₄ /4/ exhibit complex Mössbauer spectra. The positions of the individual lines range from 0.82 to 3.0 mm/s and the average isomer shift \(\overline {IS} \) derived for each compound of Sn atomic percentage x follows the relationship: \(\overline {IS} = 0.60 + 0.0194 x\) . Rather large quadrupole splittings are obtained. The f factors are about 0.20 at 295 K and 0.37 at 78 K, from which Debye temperatures of 200 to 300 K have been calculated.     

Mössbauer study of internally oxidized silver-tin alloys

A Mössbauer study of internally formed oxides as a function of oxidation temperatures between 200 C and 850 C was performed on previously annealed 1 at%AgSn alloys. The oxide formed at high temperatures (t 500 C) consists in agglomerates of tin dioxide = 0.00 ± 0.01 mm/s, Q=0.50 ± 0.03 mm/s). The low temperature oxide (t 300 C) is characterized by = 0.29 ± 0.02 mm/s and Q=0.32 ± 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t 550 C, the maximum contribution of the silver matrix to the effective number of electrons per Sn atom in oxide agglomerates has been estimated have a value of about 0.06. The effect of the cold work on the hyperfine parameters of the oxidized tin has also been investigated. As rolled samples were found to attain the same values of isomer shifts and quadrupole splittings as annealed specimens, but at lower temperatures.     

Mössbauer studies of the layered compound 1T-TAS2

We report the temperature dependence in Tantalum Disulfide 1T-TaS₂ of the elastic and inelastic intensities of the first order satellite (1.285, 0, 0.333) and (3, 0, 0.21) near the Bragg peaks (1, 0, 0) and (3, 0, 0), respectively. The phason temperature factor has been measured as a function of temperature from 70 to 295 K using Mössbauer gamma-ray scattering. The high-energy resolution provided by this technique allowed experimental separation of the elastic scattering from the inelastic thermal diffuse scattering. The first order satellite is found to be 15% inelastic. The results were compared with those found by Chapman and Colella obtained by X-ray method (Moret and Colella, Phys. Rev. Lett. 52:652, 1984).     

Mössbauer study of spin states in amorphous Fe100−x Zr x alloys

Spin states in amorphous Fe_100–x Zr_x (7x12) are investigated using hyperfine field distributions (HFDs) as derived from⁵⁷Fe transmission Mössbauer experiments. The existence of low-, medium- and high-spin states is demonstrated by three-dimensional projections of HFDs. Temperature dependences of the corresponding average values revealed anomalous behaviour in the vicinity ofT _fc. An increase in the hyperfine magnetic fields observed towards low temperatures is discussed in terms of a ferromagnet-to-spin-glass transition. Utilizing also theT _c values, which were obtained from a thermal scanning Mössbauer technique, we propose a diagram of spin states in amorphous Fe-Zr.     

A Mössbauer effect study of the Fe2+x Mn1–x Al Heusler alloys

In this work the Mössbauer spectroscopy has been used to study the magnetic properties of Fe_2?+?x Mn_1???x Al alloys with small deviations of composition from the stoichiometric 2:1:1. The Mössbauer parameters obtained for the L2₁ phase indicate H _hf fields of about 25 T and 30 T at 80 K for Fe atoms at X sites in the ordered X₂YZ structure of the L2₁ full Heusler alloys.     

Mössbauer studies of prehistoric Cherokee pottery sherds

Mössbauer spectroscopy is a very useful tool in the examination and characterization of ancient pottery sherds. In this study, Mössbauer spectra for sherds and clay from the Warren Wilson Site, a prehistoric Native American (Cherokee) settlement in western North Carolina, were measured. Data from one sherd and samples from two clay beds indicate that the sherd was not made from local clays and was originally fired to 350 C.     

Mössbauer and susceptibility studies of FeMoVO7

The oxidic phase FeMoVO₇ of the Fe₂O₃-V₂O₅-MoO₃ system has been synthesized. Susceptibility measurements from 4.2 K to room temperature display an antiferromagnetic behaviour with an effective magnetic moment of 5.80 _b . This value, and the measured Mössbauer isomer shift of 0.40±0.02 mm/s, are characteristic of high-spin Fe(III). The lowT _n value of 15 K suggests a weak interaction among the Fe-O polyhedra. The relative small QS=0.28±0.02 mm/s found in this compound shows that the Fe-O polyhedra symmetry is close to octahedral and almost undistorted.     

Mössbauer and PAC studies of nanocrystalline Fe

High-purity Fe powder was mechanically milled under argon at ambient temperature using an SPEX 8000 mill. The local atomic and magnetic structure was studied using⁵⁷Co/Fe Mössbauer and¹¹¹In/Cd perturbed angular correlations (PAC) spectroscopies. After 32 hours of milling, X-ray diffraction revealed effective grain diameters of 18 nm and energy-dispersive X-ray analysis indicated a Cr impurity concentration of 5%, presumably introduced by mechanical attrition of steel ball bearings used for milling. In addition to a spectral component very similar to bulk iron metal, the Mössbauer spectra exhibited hyperfine field shifts attributed to the Cr impurities. PAC spectra on Fe milled for 5 h, with no contamination, exhibited two components: (1) A slightly broadened magnetic interaction attributed to interior, defect-free sites of In/Cd probes with a mean hyperfine field slightly greater than in macroscopic grains. The defect-free site fraction grew appreciably during milling, even though In is essentially insoluble in Fe. (2) An indistinct signal due to mixed magnetic and quadrupole interactions attributed to probes at surface or other defect sites.