Mössbauer Study of El-Bahrain Meteorite

Procedures for the determination of traces of rare earth elements (REE) in geological samples by instrumental neutron activation analysis (INAA) and high resolution liquid chromatography (HPLC) are presented. The international standard reference materials AGV-1, GSP-1 and G-2 (USGS) were tested for the determination of REE concentrations using both techniques. The results obtained showed good agreement with certified values, giving relative errors less than 10%. By using INAA, the REE La, Ce, Nd, Sm, Eu, Tb, Yb and Lu were determined. All the REE, except Dy and Y, were determined when HPLC was employed. The application of INAA and HPLC to the determination of REE in geological samples is also discussed.     

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.     

Analysis of the Probability of the Mössbauer Effect in Iron(III) β-Diketonates

The probability of the Mössbauer effect f has been evaluated and the Debye temperatures of intermolecular vibrations _M at 295 and 78 K have been determined for ten Fe(III) -diketonates, which are complexes of molecular type. Variation of _M with temperature and molecular mass M has been found; in the latter case, _M decreases as M increases. As a result of this antibatic change in _M and M, the effect of a decreased energy of intermolecular interaction dominates the effect of increased molecular mass, and f decreases in conformity with the prediction provided by the molecular crystal model.     

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.     

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.     

Mössbauer Investigation of Characteristic Distribution of Iron Oxides in Sediments from the Antarctica

Sediments from the Admiralty Bay, King George Island, Antarctica, were investigated by ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry, and radiometry. Quartz, feldspar, chlorite, calcite, dolomite, mica, kaolinite, hematite and magnetite were identified as constituent minerals in the sediment samples. The phase composition and the iron distribution among the crystallographic sites of iron-bearing minerals (silicates, magnetite and hematite) of samples from different location have been derived from the complex Mössbauer spectra. At different locations sediments had significant characteristic differences in the mineral composition, in the iron distribution among the crystallographic site of silicates, and in the specific radioactivity of Cs radionuclides. These results indicate differences in the rock formation and alteration by the sediments in this maritime part of Antarctica. There is a much higher amount of iron oxides in the sediments from south part of the geological fault across the Admiralty Bay than in the north part. This can be associated with much more alteration in the rocks in the south part compared to the northern one. This finding can contribute to the question of the history of the formation and alteration of volcanic rocks in the border of Antarctica.     

151Eu Mössbauer Study of Calcium Aluminate Glass and Glass Ceramics Containing a Small Amount of Europium(III)

¹⁵¹Eu Mössbauer spectrum of IR-transmitting calcium aluminate glass, 60CaO·32Al₂O₃·5Fe₂O₃·3Eu₂O₃, consists of a broad peak due to distorted Eu(III) with and values of 0.91 and –2.02 mm·s^–1, respectively. Debye temperatures (_D) of 360 and 320 K were obtained from the temperature dependence of absorption area (A) and that of , respectively. These _D values indicate that Eu(III) atoms occupy substitutional sites of distorted Al(III)O₄ tetrahedra in calcium aluminate glass. The value of 0.62 mm/s obtained from the heat-treated sample (glass ceramic) indicates that Eu(III)-O bonds became less covalent. A smaller value of –1.20 mm·s^–1 was obtained for Eu(III) in the glass ceramic, indicating less distorted Eu(III)O₄ tetrahedra.     

X-Ray Diffraction and 57Fe Mössbauer Study of Iron(II) n-Butylboronate Dichloroglyoximate in a Wide Temperature Interval

The crystal and molecular structure of the clathrochelate complex Fe(Cl₂Gm)₃(BBu ⁿ )₂([tris(-1,2-dichloro-1,2-ethanedionedioximato-O:O")di-n-butyldiboronato-2)-N-N₁,N₂,N₃,N₄,N₅-iron(II)) were solved by X-ray diffraction analysis at 180, 208, 250, and 298 K. A model for the dynamic temperature-dependent disorder of the macrobicyclic ligand was proposed based on an analysis of packing and molecular geometry and on the data of calorimetry and ⁵⁷Fe Mössbauer spectroscopy.     

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.     

57Fe Mössbauer, XRD and DTA Study of the Crystallization Behavior of Calcium Aluminate Glass Containing Iron(III)

Certifications of trace elements in existing CRMs, especially biological CRMs, are far from satisfactory. Neutron activation analysis (NAA) for its inherent advantages combined with newly established parametric standardization, may contribute to improve this situation. The continuing progress of the hybrid extended k ₀-relative NAA technique developed in our laboratory is discussed. Examples are given to show the reliability of the method in certification of multielements. RNAA is still one of the best methods, or even the method of choice, in analysis at sub-g/g concentration levels. The suitability of the technique for this purpose has been studied through the determination of rare earth elements at ng/g concentration level in two Chinese biological CRMs using both RNAA and ICPMS. Sampling behaviors of multielements in CRMs have been studied by INAA in an effort to develop CRMs suitable for analysis with small sample sizes.     

Theoretical Study of Deoxygenation of Esters on Small Pt–Sn Intermetallic Clusters

Kinetics and Catalysis - The mechanisms of reactions occurring during deoxygenation of esters on Pt and intermetallic Pt–Sn catalysts (hydrodeoxygenation (stepwise and concerted mechanisms);...     

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.     

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.     

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 spectra of ferrous salts of transition metal cyano complexes. A survey

Ferrous salts of ten hexacyanometallates and three tetracyanometallates were obtained and their Mössbauer spectra interpreted according to recent structural models for these families of compounds. Ferrous ferrocyanide (Williamson White) and its ruthenium and osmium analogs prepared mechanochemically are stable for hours, allowing their study by Mössbauer spectroscopy and other related techniques. For ferrous salts of trivalent hexacyanometallate anions, the random distribution of anion vacancies is discarded and a model of two well defined relative positions of CN and H2O ligands around the Fe2+ is suggested. Iron was found octahedrally coordinated in tetracyanometallates.     

Parameters and Form of the Mössbauer Spectra of Iron(III) β-Diketonates: New Data

Mössbauer spectra have been measured at 295 and 78 K for ten ⁵⁷Fe-enriched iron(III) -diketonates differing in the type of radical in the chelate ring. Since the literature data for compounds of this class are incomplete and contradictory, a repeated analysis of spectrum shape and parameters has been performed. The chemical shift and quadrupole splitting are virtually independent of the type of radical in the chelate ring whereas the line width and asymmetry exhibit a pronounced dependence on the temperature and composition of the compounds. The available concepts on the nature of quadrupole splitting and relaxation mechanisms determining the lineshape for the given compounds are refined. It is concluded that electron spin relaxation is longitudinal or transverse relative to the principal axis of the electric field gradient in different compounds.     

Mössbauer Spectroscopy and Radiofrequency Absorption Investigations of Pr Substituted 1-2-3 Type Compounds

⁵⁷Fe and ¹⁵¹Eu Mössbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu_1–x Pr _x Ba₂Cu₃O_7– and EuBa_2–x Pr _x Cu₃O_7–, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of ⁵⁷Fe Mössbauer spectroscopy. It was found that there exists a correlation between the ¹⁵¹Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.