In situ — High Temperature Mössbauer Spectroscopy of Iron Nitrides and Nitridoferrates

The stoichiometric iron nitrides γ′‐Fe₄N, ε‐Fe₃N and ζ‐Fe₂N were characterized by Mössbauer spectroscopy. The thermal decomposition of ε‐Fe₃N was studied in‐situ by means of a specially developed Mössbauer furnace. We found ε‐Fe₃N to γ′‐Fe₄N and ε‐Fe₃N_x (x ≥ 1.3) as decomposition products and determined the border of γ′/ε transformation at T ? 930 K. Mössbauer spectroscopy was applied to study in‐situ the thermal decomposition of the nitridometalate Li₃[Fe^IIIN₂] and the formation of Li₂[(Li_1‐xFe^I_x)N], the compound with the largest local magnetic field ever observed in an iron containing material. The kinetics of formation and the stability of Li₂[(Li_1‐xFe^I_x)N] was of particular interest in the present study.     

Fifty Years of Mössbauer Spectroscopy in Solid State Research – Remarkable Achievements,Future Perspectives

Mössbauer spectroscopy was founded more than fifty years ago based on an outstanding discovery by the young German physicist Rudolf Ludwig Mössbauer while working on his Ph.D. thesis. He discovered the recoilless nuclear resonance fluorescence of gamma radiation and was awarded the Nobel Prize in Physics in 1961 as one of the youngest recipients of this most prestigious award. His discovery led to the development of a new technique for measurements of hyperfine interactions between nuclear moments and electromagnetic fields. This method, with highest sharpness of tuning of 10^–13, yields information on valence state, symmetry, magnetic behavior, phase transition, lattice dynamics and other solid state properties.     

Mössbauer Spectroscopic Studies of Ferrocenylaldimines and their TCNQ Complexes

A series of ferrocenylaldimines (Fc-CH=N-R) has been prepared by Schiff base condensation of formylferrocene with polyacenylamines RNH₂ where R = naphthyl, 5,6,7,8-tetrahydronaphthyl, anthracenyl, and pyrenyl groups. This step was followed by oxidation with TCNQ to give [Fc-CH = N-R][TCNQ]² salts. The electronic state of iron in these compounds was investigated by means of⁵⁷Fe Mössbauer spectroscopy.     

Iron speciation in natural hyperacid water investigated by Mössbauer spectroscopy

We have demonstrated the usefulness of the archetypical solid state-technique of Mössbauer spectroscopy to non-invasive studies of the redox and coordination chemistry of iron in a natural hyperacid solution from Iron Mountain, CA. Suitable fast cooling conditions were used to prepare a glass from the natural solution. Measurements of spectra at low temperatures (6 and 15 K) and in large external magnetic fields (6 T) of the glassy, frozen solution revealed a behaviour characteristic of slow paramagnetic relaxation of ferric ions. Analyses of the spectral components are in good agreement with dominance of hexaaquairon(III) ions.     

Mössbauer and Electrochemical Studies of Bridged Biferrocenes and Biferrocenylenes

A series of neutral and oxidized π-bridged biferrocenes (Fc—x—Fc) and biferrocenylenes (FC(—x—)₂Fc) (x= —CH=CH—, —CH₃,C=CCH₃—) were prepared and their physical properties have been studied by means of Mössbauuer and cyclic voltammetry. The electrode reaction of these bridged ferrocene derivatives appears to involve a consecutive two-step oxidation process. The results also show that the voltage difference between the first and second oxidaton potentials of the bridged biferrocenes was found to be largely exceeded that founded for the corresponding the bridged biferrocenylenes. The Mössbauer data show that the oxidation of doubly bridged Fc(—x—)₂Fc with iodine, DDQ, and TCNQ given the corresponding dioxidized salts only and no stable mixed-valence compounds were found.     

Mössbauer Spectroscopic Studies of the Hydroxofluorostannate(IV) Complexes

Mössbauer isomer shifts of ¹¹⁹Sn in a series of complexes K₂Sn(OH)_6-mF_m observed at 78 K were ?0.05, ?0.05, ?0.24, ?0.27 and ?0.40 mm s^?1, respectively, for m=0, 2, 4, 5 and 6. These IS values were linearly related to both m and (the average Pauling electronegativity of the ligands): . The IS straight line was compatible within experimental error with the one reported by Parish and Row-botham for the hexahalogenostannate complexes SnX₄Y₂², namely, The revised IS straight line including both series of complexes could be expressed by the equation Quadrupole splittings observed in the complexes of m = 2,4 and 5 were 1.16, 0.80 and 0.73 mm s^?1 respectively. They were linearly related to both m and .     

An in‐situ Mössbauer Study of the Formation of Cementite,Fe3C

The formation of cementite, Fe₃C, from thin iron foils has been studied at 550 and 650 °C by means of in‐situ Mössbauer spectroscopy. At 550 °C, the kinetics of the reaction have been determined from time‐resolved experiments performed at different carbon activities. The product formation follows a two‐step process exhibiting two different kinetic regimes. The slow initial stages of the reaction as well as its rapid final part can be described by an Avrami‐type kinetics with a characteristic parameter of n = 3/2.     

Magnetic Investigations and 151Eu Mössbauer Spectroscopy of MYbSi4N7 with M = Sr,Ba, Eu

The isotypic nitridosilicates MYb[Si₄N₇] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)₂ in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si₄N₇] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN₃)₄] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si₄N₇] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μ_B per formula unit. In EuYbSi₄N₇ the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state Yb^III‐x in the strontium and barium compound. Consequently, either a partial exchange N^3—/O^2— resulting in compositions MYb^III‐x[Si₄N_7—xO_x] or an introduction of anion defects according to MYb^III‐x[Si₄N_7—x/3□_x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. ¹⁵¹Eu Mössbauer spectra of EuYb[Si₄N₇] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s^—1 subject to quadrupole splitting of ΔE_Q = 5.7(8) mm s^—1, compatible with purely divalent europium.     

Electrodeposition and Mössbauer Spectra of Fe-Zn Alloys on Aluminum Foil

By controlling the current density, pH and temperature of the electrodepositing iron-zinc bath, various compositions of electrodeposited Fe_1-xZn_x (0.95 > x > 0.15) alloys on Al-foil have been prepared. The electronic state, intermetallic phases and magnetic hyperfine interactions have been studied by means of ⁵⁷Fe Mössbauer spectroscopy at 298K for these electrodeposited Fe-Zn alloys. The isomer shifts obtained from the Mössbauer spectral of the alloys increased with increasing Zn content. An alloy containing above 50% Fe, exhibits a linear dependence of the internal magnetic field, Hin, on the Zn content.     

Mössbauer Spectra and Magnetic Properties of Polydiimine Complexes of Iron(II) Sulfate

A new series of polynuclear iron complexes with polydiimine ligand have been prepared from the Schiff-base condensation of pyridine-2, 6-dialdehyde or 2, 6-diacetylpyridine with aliphatic diamines. The structures of the complexes are represented by [?N = CR-Py-CR = N-(CH₂)_n-]₂FeSO₄·xH₂O; where R = H, CH₃; n = 4?10, × = 5～8. Mössbauer spectra and magnetic measurements show several complexes have unusual magnetic properties.     

Concentration Dependence of Mössbauer Parameters of SnCl−3 and SnBr−3 Complex Ions

Mössbauer parameters of frozen salt solutions could be correlated with apparent degree of dissociation, γ. KSnCl₃ and KSnBr₃ were dissolved in 0.5 M H₂SO₄, whereas NH₄ SnCl₃ was dissolved in 0.5 M HClO₄. Mössbauer studies were made at different concentrations.     

Mössbauer Spectroscopic Studies of Chlorostannate(II) Complexes in Frozen Aqueous Solutions

Mössbauer parameters of frozen aqueous solutions of Sn(ClO₄)₂ in 0.5 M HClO₄ did not change with the concentration of NaClO₄, so that it was used to keep the ionic strength at the desired level. When NaCl was added into Sn(ClO₄)₂ solutions, isomer shift did not change, but quadrupole splitting did. Therefore, stability constants were calculated from the quadrupole splitting data, which were in good agreement with the published values. The observed spectra could be resolved into components.     

Mössbauer Spectroscopic Studies of Bromostannate(II) Complexes in Frozen Aqueous Solutions

Mössbauer spectra of KSnBr₃·2H₂O were very broad and could not fit Lorentz equation, suggesting unresolvable quadrupole doublets. Its quadrupole splitting was estimated to be about 0.25 mm/s from the separate experiments on frozen aqueous solutions of Sn(II)-Br^? systems. Stability constants of bromostannate(II) complexes were determined at μ = 3.5 from the Δ-c_L curve by the approximation method, which were in agreement with the literature values.