Mössbauer Study of the Structure of Fe - Zircon System

Iron-doped silicate (zircon), prepared by a ceramic method with the addition of LiF as mineralizer, was analyzed by X-ray powder diffraction (XRD) and ⁵⁷Fe Mössbauer spectroscopy to obtain information on the solid solution formation. The results of X-ray diffraction and Mössbauer spectroscopy have shown that only a small fraction of iron, about 1.5 mol%, is incorporated in the zircon structure as paramagnetic Fe³⁺ species while the remaining Fe³⁺ cations form magnetic -Fe₂O₃ particles which are trapped within the zircon matrix.     

Theoretical Study on Mössbauer Isomer Shift of Layered Compounds

Using the expended chemical bond dielectric theory of complex crystals, we have calculated chemical bond parameters and Mössbauer isomer shift of LnOFeAs as well as AFe₂As₂ which had been chosen due to their layered structures. Results are in good agreement with available experimental data, demonstrating the accuracy of our calculations and theories. The relationship between chemical bond parameters and Mössbauer isomer shift is discussed.     

Mössbauer Spectroscopy of Spinels

Soon after the discovery of the Mössbauer effect, studies were performed on spinels containing various transition metal ions (mostly Fe²⁺). This method proved very useful for investigating the local symmetry at transition metal ions. In spite of the numerous results, the correct interpretation of the complex quadrupole split spectra is still not given for numerous spinel structures. Since spectra of different shapes were measured for FeAl₂O₄ and FeCr₂O₄ by different authors, we performed new measurements on these spinels. The results on FeAl₂O₄ showed that the statistical distribution of another kind of ions in the positions A may influence the electric field gradient at the Fe²⁺ ions in the tetrahedral interstices. In FeCr₂O₄ and in the mixed Fe_0.5Mg_0.5Cr₂O₄, the electric field gradient exists at the Fe²⁺ ions at room temperature indicating that the degeneracy of the orbital doublet of the Fe²⁺ is removed.     

Study of the dependence of Mössbauer parameters on the outer cation in nitroprussides

The Mössbauer spectra of 29 nitroprussides have been measured and the parameters and correlated with the polarizing power Z/r² of the outer cations. There is no overall correlation but there are limited groups in which a trend can be ascertained. In isoelectronic sequences such as Li⁺, Be²⁺; Mn²⁺, Fe³⁺, where the outer electronic shell remains fixed, while Z/r² increases, a definite trend of decreasing and with increasing Z/r² is observed.     

Mössbauer study of iron-containing atmospheric aerosols

The Mössbauer technique was applied to study the seasonal variations of iron concentration in atmospheric air. The concentration of iron in air was calculated by the area method from the experimental spectra obtained. From the shapes of the Mössbauer spectra it was concluded that iron appears as Fe₂O₃ in the form of ultrafine particles in the superparamagnetic state. The measurements as a function of temperature [from 300 to 75 K) made it possible to estimate the size of iron-containing aerosol particles. Correlation of the seasonal variations of iron concentration with meteorite activity was discussed. This method was applied also in investigations of iron concentration variations with air radioactivity due to nuclear explosions performed in the atmosphere. Attempts were made to find a relation between air pollution and the concentration of iron in the air.     

On the calculation of Mössbauer isomer shift

A quantum chemical computational scheme for the calculation of isomer shift in Mossbauer spectroscopy is suggested. Within the described scheme, the isomer shift is treated as a derivative of the total electronic energy with respect to the radius of a finite nucleus. The explicit use of a finite nucleus model in the calculations enables one to incorporate straightforwardly the effects of relativity and electron correlation. The results of benchmark calculations carried out for several iron complexes as well as for a number of atoms and atomic ions are presented and compared with the available experimental and theoretical data.     

Mössbauer studies of the alkaline-earth ferricyanide hydrates

The existence of alkali-earth ferricyanides hydrates with different number of water molecules is established by the Mossbauer effect, thermogravimetric and differential thermal analysis. The Mössbauer spectra exhibits a quadrupole splitting whose value is dependent on the number of water molecules in the unit cell. It is shown that the hydration process is not a continuous one but the loss or gain of water molecules occurs by steps in a well defined way.     

Mössbauer study of Japanese ancient iron slag

Mössbauer spectroscopy was applied to an investigation of ancient iron slags, excavated at the ancient ruins for iron manufacturing in order to deduce the raw materials and operative conditions of the furnace. From the Mössbauer spectra, it was found that the slags consisted of fayalite, wüstite, ulvöspinel and magnetite.     

Mössbauer study of some Fe-containing M6 and M5 clusters

Isomer shift (δ) and quadrupole splitting (Δ) parameters have been assigned to the iron sites in [FeRh₅(CO)₁₆]⁻, trans- and cis-[Fe₂Rh₄(CO)₁₆]²⁻, [Fe₃-Rh₃(CO)₁₇]³⁻, [FeRh₄(CO)₁₅]²⁻, [Fe₃Pt₃(CO)₁₅]²⁻ and [Fe₄M(CO)₁₆]²⁻ (M = Pd or Pt) from ⁵⁷Fe Mössbauer spectra recorded at 78 K. The data for the closo compounds [FeRh₅(CO)₁₆]⁻ and [Fe₂Rh₄(CO)₁₆]²⁻ are compared with those for [Fe₆(CO)₁₆C]²⁻. In [Fe₃Rh₃(CO)₁₇]³⁻, the three major Fe sites were identified. For both [Fe₄M(CO)₁₆]²⁻ compounds two isomers were shown to be present in the solid state.     

A study of carbonic anhydrase using Mössbauer spectroscopy

The preparation and characterization of an Fe(II) bovine carbonic and human carbonic anhydrase are presented. Results of Mössbauer spectroscopy measurements indicate that the Fe(II) (low spin) is bound at the enzymatically active site. The results are compared with previous studies which had used the technique of perturbed angular correlations of γ-radiation.     

A study of XeFeF9 from Mössbauer spectra

A study of the new antiferromagnetic complex XeFeF₉ by the Mössbauer effect has contributed experimental data on the temperature dependence of hyperfine splitting parameters of ⁵⁷Fe. There is evidence that the relative intensity of the lines is affected by the texture. The anomalous spectra in the range 85 – 100 K might be interpreted as superparamagnetism; the corresponding blocking temperature being obtained near 98 K.     

Mössbauer Spectroscopy of Iron Oxides and Related Compounds

The superparamagnetic iron oxide particles with a diameter of about 10 and 16 nm were obtained by the reaction of Fe²⁺ and Fe³⁺ ions in a water pool of reversed microemulsions. The obtained particles were ascribed to -Fe₂O₃ due to the oxidation of Fe₃O₄. Very fine particles of -Fe and Fe₃O₄ were also obtained by the thermal decomposition of FeC₂O₄2H₂O. The decomposition products and their particle size depended on the heat treatments.     

Variable-temperature 119Sn Mössbauer study of tin phthalocyanines

Variable-temperature ¹¹⁹Sn Mössbauer spectroscopic (VTMS) data for six tin phthalocyanine (pc) derivatives have been collected in order to ascertain the restrictions imposed by the macrocyclic ring on the vibrational motion of the tin atom. Thermal condensation of [(t-Bu)₄pc]Sn(OH)₂ yields the co-facially stacked polymer {[(t-Bu)₄pc]SnO}_n which can be distinguished in the VTMS experiment by the enhanced rigidity of its structure.     

Applications of Mössbauer spectroscopy to the study of electronic materials

A brief introduction to the methodology of the Mössbauer spectroscopy will be given. The main applications to the study of the intrinsic properties of the materials employed in the electronic technology are reviewed.The reported examples prove the effectiveness of this techniques in the study of semiconducting and magnetic materials.Evidence will be given also to the studies of preparation processes of crystalline and amorphous compound.     

Mössbauer study of the new pyrochlore form of FeF3

Mössbauer spectrometry has been undertaken as a function of temperature on a new form of FeF₃ with the modified pyrochlore structure, recently synthesized by topotactic oxidation. The Mössbauer data (in zero field and in external magnetic field) lead to a noncollinear magnetic structure, in agreement with previous neutron diffraction results. The low value of T_N is discussed in terms of magnetic frustration.     

Mössbauer measurements on iron phthalocyanines

Monomeric and polymeric iron phthalocyanines (FePc) with and without carbon support and subjected to various heat treatments have been studied by Mössbauer spectroscopy. Dispersing FePc on carbon changes the electronic state of the monomer to low spin (S = 0) while the electronic state of the polymer remains unchanged (S = 1). It is suggested that the bonding between polymeric FePc and carbon takes place through the side groups present on the peripheral parts of the polymer and/or through suitable chemical groups present on the carbon surface. The electron-attracting ability of the side-groups deduced from the Mössbauer spectra is discussed. The results will form a basis for a comparison with data from electrochemical measurements.     

The Mössbauer effect in hexafluorostannates

Journal of Structural Chemistry -     

Mössbauer effect in dehydrated nitroprussides

Mössbauer spectra were obtained for hydrated and dehydrated sodium, potassium, lithium, cobalt, cadmium, nickel, zinc, manganese and ferrous nitroprussides. All spectra except for ferrous nitroprusside consisted of two dips separated by an amount ranging from about 1.7 to 1.9 mm/sec. In most cases the isomer shift decreased and the quadrupole splitting increased after the compound was dehydrated. The spectrum of ⁵⁷Fe-enriched ferrous nitroprusside contained eight dips. Linear bridging from the nitroprusside anion to the iron cation is a possible explanation for the complicated spectrum.