Mössbauer study of Fe in 3C-SiC following 57Mn implantation

Our investigations on substitutional and interstitial Fe in the group IV semiconductors, from ⁵⁷Fe Mössbauer measurements following ⁵⁷Mn implantation, have been continued with investigations in 3C-SiC. Mössbauer spectra were collected after implantation and measurement at temperatures from 300 to 905 K. Following comparison with Mössbauer parameters for Fe in Si, diamond and Ge, four Fe species are identified: two due to Fe in tetrahedral interstitial sites surrounded, respectively, by four C atoms (Fe_i.C) or four Si atoms (Fe_i,Si) and two to Fe in (or close to) defect free or implantation damaged substitutional sites. An annealing stage at 300–500 K is evident. Above 600 K the Fe_i,Si fraction decreases markedly, reaching close to zero intensity at 905 K. This is accompanied by a corresponding increase in the Fe_i,C fraction.     

57Fe hyperfine interactions in M1 and M2 sites of olivine from Omolon meteorite: study using Mössbauer spectroscopy

Study of olivine (Fe, Mg)₂SiO₄ from Omolon meteorite was performed using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. Components related to ⁵⁷Fe in crystallographically non-equivalent M1 and M2 sites in olivine were determined and its Mössbauer hyperfine parameters were evaluated at both temperatures. A Fe^2?+?–Mg^2?+? distribution coefficient and a temperature of cation equilibrium distribution for olivine from Omolon were evaluated on the basis of Mössbauer parameters.     

Identification of substitutional and interstitial Fe in 6H-SiC

Iron impurities on interstitial (Fe_i) and substitutional sites (Fe_S) in SiC have been detected by ⁵⁷Fe emission Mössbauer spectroscopy following implantation of radioactive ⁵⁷Mn⁺ parent ions. At temperatures <900 K two Fe_i species are found, assigned to quasi-tetrahedral interstitial sites surrounded by, respectively, four C (Fe_i,C) or Si atoms (Fe_i,Si). Above 900 K, the Fe_i,Si site is proposed to “transform” into the Fe_i,C site by a single Fe_i jump during the lifetime of the Mössbauer state (T _1/2?=?100 ns). Fe_i,C and substitutional Fe_S sites are stable up to >1,070 K.     

Mössbauer study of spin structure transformation from an incommensurate to a commensurate state

We present crystallographic and magnetic properties of NiCr_1.98 ⁵⁷Fe_0.02O₄ by using X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. The lattice constants a₀ were determined to be 8.318 Å. The ferrimagnetic Neel temperature (T _N) for NiCr_1.98 ⁵⁷Fe_0.02O₄ is determined to be 90 K. The Mössbauer absorption spectra for all chromites at 4.2 K show two well developed sextets superposed with small difference of hyperfine fields (H _hf) caused by Cr^3?+? ions in two different magnetic sites. The values of the isomer shifts show that the charge states of Fe are Fe^3?+? for all temperature range. Ni-chromites Mössbauer spectra below T _N present aline broadening due to a Jahn–Teller distortion and show that spin structure behavior of Cr ions change from an incommensurate to a commensurate state.     

Characterization of Fe states in dilute 57 Mn implanted SnO 2 film

States of dilute Fe in SnO₂ have been monitored using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of ⁵⁷Mn (T _1/2 = 85.4 s) in the temperature range from 143 K to 711 K. A sharp annealing stage is observed at ~330 K where the Fe^3?+?/Fe^2?+? ratio shows a marked increase. It is suggested that this annealing stage is due to the dissociation of Mn-V_O pairs during the lifetime of ⁵⁷Mn; the activation energy for this dissociation is estimated to be 0.9(1) eV. Fe^3?+? is found in a paramagnetic state showing spin-lattice relaxation rates consistent with an expected T ² dependence derived for a Raman process. In addition, a sharp lined doublet in the Mössbauer spectra is interpreted as due to recoil produced interstitial Fe.     

Formation of Fe i –B pairs in silicon at high temperatures

We report on the detection of Fe _i –B pairs in heavily B doped silicon using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of radioactive ⁵⁷Mn⁺ parent ions (T _1/2?=?1.5 min) at elevated temperatures >?850 K. The Fe _i –B pairs are formed upon the dissociation of Fe _i –V pairs during the lifetime of the Mössbauer state (T _1/2?=?100 ns). The resulting free interstitial Fe_i diffuses over sufficiently large distances during the lifetime of the Mössbauer state to encounter a substitutional B impurity atom, forming Fe _i –B pairs, which are stable up to ～1,050 K on that time scale.     

Effect of FeCl3 and acetone on the structure of Na–montmorillonite studied by Mössbauer and XRD measurements

⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy and infrared spectroscopy were used to study the effect of FeCl₃ and acetone on the structure of a Na–bentonite. XRD indicated the incorporation of Fe³⁺ ions into the interlayer space since the basal lattice spacing of montmorillonite increased to 1.6 from 1.24 nm after treatment with FeCl₃ dissolved in acetone. Interlayer Na⁺ ions could be exchanged to Fe³⁺. Magnetically split Mössbauer subspectra with internal magnetic fields 41 and 46 T at 74 K, were associated with two main Fe³⁺ microenvironments within the interlayer regions. The resultant Fe–montmorillonite was successfully applied as a catalyst in the preparation of 1,1-diacetates from aromatic aldehydes and acetic acid anhydride.     

Isotope-selective laser photodetachment for 129I accelerator mass spectrometry

2D coordination polymer iron(II) spin crossover complexes containing 3,5-lutidine with host framework Fe(3,5-lutidine)₂Ni(CN)₄were synthesized. Their spin crossover properties were studied by temperature dependent ⁵⁷Fe Mössbauer spectroscopy. Materials show gradual incomplete spin crossover with distinct thermochromism, while only 25 % of iron(II) ions are switched to the low spin state at 80 K, as determined by a detailed ⁵⁷Fe Mössbauer study.     

Mössbauer Effect Study of Eu0.88Fe4Sb12 Skutterudite

The partly filled skutterudites Eu_0.88Fe₄Sb₁₂ were investigated by ⁵⁷Fe Mössbauer spectroscopy in the temperature range 4.2 K ≤ T ≤ 295 K and in external fields up to 13.5 T. The results favour a statistical distribution of Eu and voids in the Fe near neighbour shell. Below 82 ± 1 K magnetic order is present. Debye temperatures Θ _D = 460 ± 20 K and 165 ± 30 K were obtained for Fe with completely occupied Eu sites and for Fe with vacancies in the R-neighbour shell, respectively. The temperature dependence of the quadrupole splitting reflects the thermal expansion of the lattice. The induced hyperfine fields at 4.2 K are negative and differ by roughly a factor of two for the two Fe surroundings.     

Mössbauer study of iron uptake in cucumber root

⁵⁷Fe Mössbauer spectroscopy was used to study the uptake and distribution of iron in the root of cucumber plants grown in iron-deficient modified Hoagland nutrient solution and put into iron-containing solution with 10 μM Fe citrate enriched with ⁵⁷Fe (90%) only before harvesting. The Mössbauer spectra of the frozen roots exhibited two Fe³⁺ components with typical average Mössbauer parameters of δ?=?0.5 mm s^?1, Δ?=?0.46 mm s^?1 and δ?=?0.5 mm s^?1, Δ?=?1.2 mm s^?1 at 78 K and the presence of an Fe²⁺ doublet, assigned to the ferrous hexaaqua complex. This finding gives a direct evidence for the existence of Fe²⁺ ions produced via root-associated reduction according to the mechanism proposed for iron uptake for dicotyledonous plants. Monotonous changes in the relative content of the components were found with the time period of iron supply. The Mössbauer results are interpreted in terms of iron uptake and transport through the cell wall and membranes.     

Mössbauer investigation of Fe0.5In1.5S3

⁵⁷Fe Mössbauer measurements are reported on a cubic spinel with nominal composition Fe_0.5In_1.5S₃ in the temperature range 4.3 K to 295 K. An occupation ratio of 0.05:1 was determined for Fe in the tetrahedral A and octahedral B positions. Below 10 K evidence for the appearance of a spin glass state is obtained.     

Magnetism of (Fe0.93Ni0.07)2P studied using 57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectroscopic measurements have been carried out on (Fe_0.93Ni_0.07)₂P in the temperature range 85–405 K. Obtained values of hyperfine field at the two metallic sites are slightly smaller than in Fe₂P. But the reduction is much less than as reported in Cr or Mn or Co substituted analogues of Fe₂P.     

Localisation of iron ions in NH4,Na-Y zeolite: A Mössbauer effect study

Localisation of Fe ions in deep-bed treated NH₄,Na-Y zeolite at 830K, 940K, and 1050K, as well as after reduction by hydrogen, and dealumination with subsequent calcination is studied by⁵⁷Fe Mössbauer spectroscopy. Most of the incorporated iron is present in the form of octahedrally coordinated ferric species with two distinct sets of hyperfine parameters assigned to atoms inside the zeolite structure and in extraframework positions. Fe²⁺ ions with high coordination are also detected and their amount increases with the temperature of deep-bed treatment. Low-temperature Mössbauer effect measurements at 77K and 4.2K were employed to facilitate the identification of iron sites.     

57Fe Mössbauer spectroscopy study of phlogopite megacrysts from an evolved carbonatitic kimberlite in the northeastern Oman Mountains

The Fe oxidation degree determined by ⁵⁷Fe Mössbauer spectroscopy and microprobe was used to characterize fresh and altered phlogopite megacrysts from an evolved carbonatitic kimberlite from northeastern Oman. The Quadrupole splitting (QS) varies between 2.19 and 2.48 mm/s (Fe^2?+?) in the fresh phlogopite samples and between 2.40 and 2.47 mm/s in the altered phlogopite samples. The quadrupole splitting of the Fe^3?+? doublets varies between 0.66 and 0.85 mm/s in the fresh samples. The altered phlogopite samples show three Fe^3?+? doublets; the first show a quadrupole splitting between 0.97 and 1.13, the second quadrupole splitting varies between 0.24 and 0.46 mm/s and the third varies between ??0.23 and ??0.35 mm/s. The phlogopite was observed to have an average Fe^3?+?/Fe_total of 35% to 37%, and corresponds to fresh phlogopite. The second one results from the alteration of the first type, and the Fe^3?+?/Fe_total ranges between 40% and 57%. Tetrahedral Fe^3?+? ions were confirmed in the altered phlogopite samples. Quantitative Fe site distributions can be obtained from room-temperature Mössbauer data if the different recoilless factors for octahedral Fe^2?+? and tetrahedral Fe^3?+? are considered. The observed isomer shifts are consistent with Mössbauer temperatures of 330 K, reported in the literature for tetrahedral and octahedral Fe^3?+? and Fe^2?+? in phlogopite. The results are compared to those obtained for natural and synthetic phlogopite from worldwide.     

Variations in quadrupole splitting of the 57 Fe in the M1 and M2 sites of meteoritic olivines with different origin

A comparative study of meteoritic olivine in bulk samples of Farmington L5 and Tsarev L5 ordinary chondrites and extracted from Omolon and Seymchan the main-group pallasites was performed using Mössbauer spectroscopy with a high velocity resolution. Mössbauer spectra for each specimen were measured at 295 and 90 K. Mössbauer spectral components related to the ⁵⁷Fe in crystallographically non-equivalent sites M1 and M2 in olivines were determined and their Mössbauer hyperfine parameters were evaluated. It was found small variations of quadrupole splitting for the ⁵⁷Fe in both the M1 and M2 sites of olivines in bulk ordinary chondrites and olivines extracted from pallasites.     

Tin-doped spinel-related oxides of composition M3O4 (M = Mn, Fe, Co)

Tin-doped compounds of spinel-related M₃O₄ (M = Fe, Mn, Co) have been studied by ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectroscopy in the temperature range of 20–600 K. The ¹¹⁹Sn Mössbauer spectra recorded down to 20 K from the non-iron-containing compounds of Co₃O₄ and Mn₃O₄ contained only doublets showing no transfer of magnetic properties from cobalt or manganese to the dopant tin ions. In contrast, the tin-doped-(FeCo)₃O₄ and (FeMn)₃O₄ gave ¹¹⁹Sn and ⁵⁷Fe Mössbauer spectra, which showed magnetic hyperfine interactions. The Curie temperature has been estimated for the former sample.     

Effect of Sn on methane decomposition over Fe supported catalysts to produce carbon

In this work, alumina-supported Sn containing Fe catalysts were investigated in CVD reactions (Chemical Vapor Deposition) using methane for carbon production. The catalysts were prepared with 10 wt.% of Fe (as Fe₂O₃) and 3, 6 and 12 wt.% of Sn (as SnO₂) supported on Al₂O₃ named hereon Fe10Sn3A, Fe5Sn6A and Fe10Sn12A, respectively. These catalysts were characterized by SEM, TPCVD, TPR, TG, Raman, XRD and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy. Methane reacts with Fe10A catalyst (without Sn) in the temperature range 680?C900°C to produce mainly Fe⁰, Fe₃C and 20 wt.% of carbon deposition. TPR and TPCVD clearly showed that Sn strongly hinders the CH₄ reaction over Fe catalyst. ⁵⁷Fe Mössbauer suggested that in the presence of Sn the reduction of Fe^?+?3 by methane becomes very difficult. ¹¹⁹Sn Mössbauer showed Sn^?+?4 species strongly interact with metallic iron after CVD, producing iron-tin phases such as Fe₃SnC and FeSn₂. This interaction Sn?CFe increases the CVD temperatures and decreases the carbon yield leading to the production of more organized forms of carbon such as carbon nanotubes, nanofibers and graphite.     

Mössbauer study of Fe‐doped CuGeO3 system Cu0.9Ge0.9Fe0.2O3

The Fe‐doped system Cu_0.9Ge_0.9Fe_0.2O₃ has been investigated by means of X‐ray diffractometry, Mössbauer spectroscopy and superconducting quantum interference device. The structure of this system is orthorhombic and the lattice constants are a=4.784 Å, b=8.472 Å and c=2.904 Å, respectively. Magnetic measurements confirm that the spin‐Peierls transition appears in our sample at about 12 K, which is near to the spin‐Peierls transition temperature (T _sp) 14 K of pure CuGeO₃ system. The Mössbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe³⁺ ions from room temperature to 4.2 K. The Mössbauer parameters show a discontinuity near T _sp. The jump of the magnetic hyperfine field at temperatures lower than T _sp means increasing of the superexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrement in symmetry of lattice sites and spontaneous thermal contraction.     

57Fe Emission Mössbauer Study on Gd3Ga5O12 implanted with dilute57Mn

⁵⁷Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet Gd₃Ga₅O₁₂ (GGG) single crystals in the temperature interval 300 – 563 K within the extremely dilute (<10^?4 at.%) regime following the implantation of⁵⁷Mn (T¹_/2= 1.5 min.) at ISOLDE/CERN. These results are compared with earlier Mössbauer spectroscopy study of Fe-doped gadolinium gallium garnet Gd₃Ga₅O₁₂(GGG), with implantation fluences between 8×10¹⁵ and 6×10¹⁶ atoms cm^?2. Three Fe components are observed in the emission Mössbauer spectra: (i) high spin Fe²⁺ located at damage sites due to the implantation process, (ii) high spin Fe³⁺ at substitutional tetrahedral Ga sites, and (iii) interstitial Fe, probably due to the recoil imparted on the daughter^57?Fe nucleus in the β^? decay of⁵⁷Mn. In contrast to high fluence⁵⁷Fe implantation studies the Fe³⁺ ions are found to prefer the tetrahedral Ga site over the octahedral Ga site. No annealing stages are evident in the temperature range investigated. Despite the very low concentration, high-spin Fe³⁺ shows fast spin relaxation, presumably due to an indirect interaction between nearby gadolinium atoms.     

Mössbauer effect of iron-57 intercalated in layered compound 2H−Fe0.5TaSe2

⁵⁷Fe Mössbauer effect study has been performed on intercalated compound 2H?Fe_0.5TaSe₂ over a temperature range between 14K and 500K. The highly concentrated intercalation samples 2H?Fe_xTaSe₂ with Fe atoms (x up to 2) are prepared by the electrochemical method for the first time. The Mössbauer measurement shows that iron is in Fe³⁺ high spin state and with the same probability occupies both octahedral and tetrahedral interstices of the Van der Waals gap. The fact that effective masses of iron ions in both sites are close to 57 amu and characteristic temperatures (Θ_M =130K, 107K respectively) are found to be relatively small is attributed to the weak forces on Fe³⁺.