Mössbauer spectroscopic investigation of tin-doped thiospinels

The tin-doped sulphur-containing compound of composition Fe_1.05Cr_1.90Sn_0.05S₄, in which tin is located on the octahedral sites as Sn^4?+? in the spinel-related structure, has been examined by ¹¹⁹Sn Mössbauer spectroscopy. The data complement results obtained by ⁵⁷Fe Mössbauer spectroscopy and show that tin increases the magnetic ordering temperature of pure FeCr₂S₄.     

High temperature Mössbauer spectroscopy of titanomagnetite and maghemite in basalts

Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (J _s -T) curves with Curie temperatures of about 840 K, has revealed considerable amounts of maghemite (-Fe₂O₃) in many samples. In view of the expected instability of maghemite at temperatures above 620 K, this reversibility came as a surprise. For further studies of the magnetization-temperature relationship of these minerals, we have constructed an elliptical radiation-heated furnace in which Mössbauer spectra can be acquired at temperatures between 300 and 900 K. Measurements at different temperatures have been obtained for two types of basalts, one in which the magnetic minerals are nearly pure magnetite and the other where the room temperature spectrum indicates a mixture of maghemite and magnetite. The two series show different features of the collapse of the internal magnetic hyperfine field, and the composition of minerals in the samples changes during the treatment, showing maghemite.     

Mössbauer study of bacterial iron-reduction processes in natural glauconite and biotite

Interaction between a bacterial monoculture of alkaliphylic G. ferrihydriticus along with binary cultures of G. ferrihydriticus and cellulolytic C. alkalicellulosi and natural biotite and glauconite under alkaliphylic conditions is investigated by means of Mössbauer spectroscopy. Measurements were performed over a range of temperatures from T = 4.8 K to T = 300 K. It was found that a new magnetically ordered phase was formed during culture growth. This new phase was a mixture of nonstoichiometric magnetite and maghemite. The relative amount of the magnetically ordered phase in the monoculture of G. ferrihydriticus when interacting with glauconite is less than in the case of the binary culture. Iron reduction glauconite is also more intense than in biotite.     

Mössbauer investigation of novel pentadentate schiff base complexes

We synthesised a series of seven mononuclear and two trinuclear Schiff base coordination compounds. All nine complexes have been analysed by Mössbauer and IR spectroscopy. The Mössbauer spectra reveal a doublet, which are related to the high spin state (S = 5/2) of the iron(III) centres.     

Use of Mössbauer effect for ion-exchange resins investigation

Results of gamma-resonance spectroscopy investigation of iron ions sorption by aminocarboxylic ampholytes ANKB-2 and ANKB-50 are presented. Conclusions on the forms of the complexes produced in the phase of hydrated ion-exchangers are drawn.     

Mössbauer spectroscopy in the investigation of new mineral–related materials

New materials based on the composition of the mineral schafarzikite, FeSb $_{2}\textit {O}_{4}$ , have been synthesised. $^{57}$ Fe- and $^{121}$ Sb- Mössbauer spectroscopy shows that iron is present as Fe $^{2+}$ and that antimony is present as Sb $^{3+}$ . The presence of Pb $^{2+}$ on the antimony sites in materials of composition FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ induces partial oxidation of Fe $^{2+}_{}$ to Fe $^{3+}$ . The quasi-one-dimensional magnetic structure of schafarzikite is retained in FeSb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ and gives rise to weakly coupled non-magnetic Fe $^{2+}$ ions coexisting with Fe $^{3+}$ ions in a magnetically ordered state. A similar model can be applied to account for the spectra recorded from the compound Co $_{0.5}$ Fe $_{0.5}$ Sb $_{1.5}$ Pb $_{0.5}\textit {O}_{4}$ .     

Mössbauer investigation of In and Sc substituted barium hexaferrite

A detail Mössbauer analysis has been performed on polycrystalline samples of hexagonal ferrites with composition BaFe_12-x In _x O₁₉ (0x4) and BaFe_12-x ScxO₁₉ (0x3). The dependence on composition of the distribution of metallic cations among the five sublattices of the structure has been determined: these data confirm the strong preference of Sc and In ions for the sites belonging to the R block.As a consequence iron ions located in the main spin up sublattice (12k) with different number of neighbouring Fe³⁺ ions display different temperature dependences of the magnetization. The occurrence of non-collinear spin configurations, even for very low degrees of substitution of iron, has also been evidenced.     

Structural transformations in NANOPERM-type alloys studied by Mössbauer spectrometry and diffraction of synchrotron radiation

As-quenched Fe_91???x Mo₈Cu₁B _x NANOPERM-type alloys (x?=?12, 15, 17, 20) were exposed to continuous heat treatment up to 800°C. During the temperature increase (ramp of 10 K/min), an in situ acquisition of diffracted synchrotron radiation intensities was performed. The obtained data are correlated with those derived from the volume and surface Mössbauer effect experiments. The onset of individual crystallization steps as well as identification of the crystalline phases created is discussed.     

The investigation of magnetic state variations in α-Fe and its alloys by means of continuous temperature scanning of the Mössbauer effect

A new method for continuous temperature scanning of the Mössbauer effect was developed permitting the measurement in a broad temperature range with satisfactory precision. The temperature dependence of Mössbauer radiation transmission for -Fe, amorphous Fe-P and for alloys was measured from 20–800°C. A region of anomalous transmission was observed for crystalline -Fe and its alloys and a new method of Debye-temperature determination was proposed.     

Mössbauer spectroscopy in catalysis

Application of in situ Mössbauer spectroscopy for studying catalysts and catalytic processes is discussed. Examples are presented to illustrate the potentials of the method by describing studies on supported heterogeneous catalysts performed with ¹¹⁹Sn and ⁵⁷Fe spectroscopies in cases with certain metals and alloys, oxides and porous substances. The results are interpreted in comparison to the catalytic performance.     

Mössbauer effect in proteins

In proteins, the M?ssbauer effect and neutron scattering show a broad line and a rapid increase of the conformational mean-square displacement above about 180?K. The increase, dubbed the "dynamical transition," is controversial. We introduce a new interpretation of the M?ssbauer effect in proteins and demonstrate that no dynamical transition is required. The increase in the mean-square displacement and the broad line are caused by fluctuations in the protein's hydration shell. Using the dielectric spectrum of these fluctuations, we predict the shape of the M?ssbauer spectrum from 80 to 295?K with one dimensionless coefficient.     

Mössbauer investigation of non-aggregated γ-Fe2O3 particles

Investigation by Mössbauer spectroscopy of non-aggregated nanometric -Fe₂O₃ particles dispersed in polymer is reported. Magnetic interactions between the particles were controlled by varying the particle concentration in the polymer. The results show that over the investigated range, the interactions make the relaxation time shorter. Infield experiments show spin canting which increases with decreasing particle size.     

Influence of the soliton in anharmonic molecular crystals with temperature on Mössbauer effect

The influence of a soliton on the properties of the M?ssbauer effect resulting from the gamma-active nuclei situated at lattice sites in quasi-one-dimensional anharmonically organic molecular chains, in which the active nuclei emit gamma-photons, has been theoretically studied by a quantum vibrational model. An expression for the gamma-radiated M?ssbauer transition probability as a function of the temperature and non-linear interaction has been obtained. Finally we give some new properties of this effect from numerical calculation in such a case, which present a way to experimentally confirm the soliton existence in molecular crystals. Received 9 April 1998 and Received in final form 11 December 1998     

Mössbauer Study of Multiple Substitutions in YBCO

Hyperfine Interactions - Mössbauer studies of multiple substitutions in YBCO with general formula (Y1?Z Ca Z )Ba2(Cu1?X?Y Fe Y M X )3O7?δ are reported. XRD has...     

Mössbauer characteristics of glauconitisation

Using 50 MeV Li^3?+? ion irradiation, the change induced in polycrystalline ferrites Li_0.5(1?+?x)Ti _x Al_0.1Fe_2.4???1.5x O₄ (x = 0.0 to 0.3, step–0.1)[LTAF] and Li_0.5(1?+?x)Ti _x Cr_0.1Fe_2.4???1.5x O₄ (x = 0.0 to 0.3, step–0.1; LTCF) in the electronic stopping power regime is studied. Both the systems were irradiated with the same fluence of 5 × 10¹³ ions/cm². The modifications of the structural and magnetic properties are studied by means of X-ray diffraction (XRD), magnetization, ⁵⁷Fe Mössbauer spectroscopy and low field a. c. susceptibility. The contrast in the role of Ti^4?+? in the presence of Al^3?+? and Cr^3?+? causing the formation of paramagnetic centres through Swift Heavy Ion Irradiation (SHII) induced cation rearrangement has been revealed through the comparative Mössbauer signatures of both the systems. The hyperfine interaction parameters deduced through Mössbauer spectra are also discussed before and after irradiation. The observed reduction in the saturation magnetic moment and Curie temperature after irradiation supports the partial formation of paramagnetic centres and rearrangement of cations in the lattice.     

Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

A Mössbauer investigation of SnO2 films with preferred orientation of crystallites

The textured SnO₂ films with different thickness in the range of 600–11200Å prepared by chemical vapour deposition (CVD) have been characterized by using conversion electron Mössbauer spectroscopy (CEMS) couping with X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The evidence for the existence of an interaction between SnO₂ and glass substrate with the formation of a interface layer about 200Å thick has been discussed. SnO₂ existing in polycrystalline state with preferred crystal face orientation is found as long as the SnO₂ films are thick than 1800Å.     

A Mössbauer investigation of zirconium distribution and diffusion in ball milled nanocrystalline iron powders

Ball milled nanocrystalline iron with minor zirconium additions was examined using ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction. Powder samples were synthesized using 0, 5, and 10 wt.% zirconium additions and milled at room temperature for periods up to 24 h. Progressive decrease in grain size as determined by X-ray diffraction was observed as a function of milling time. Mössbauer spectroscopy indicates increased iron-zirconium coordination with increased milling time. After milling, the powder samples were then heat treated in an inert atmosphere of argon at up to 925 K for various times up to 25 min. Analysis of X-ray peak line width (FWHM) was used to characterize grain size and grain growth kinetics as a function of heat treatment, milling time, and alloy content and reveal an increasingly finer post-heated structure in the alloy samples containing more zirconium. Mössbauer measurements were made and suggest Zr is steadily distributed into the Fe lattice with milling and rapidly diffuses to the grain boundaries with heat treatment. The impurity-rich grain boundaries appear to considerably stabilize the refined structure.     

Mössbauer spectroscopic study of 57Fe metabolic transformations in the rhizobacterium Azospirillum brasilense Sp245

Preliminary ⁵⁷Fe transmission Mössbauer spectroscopic data were obtained for the first time for live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (wild-type strain Sp245) grown aerobically with ⁵⁷Fe^III–nitrilotriacetate (NTA) complex as a sole source of iron. The results obtained have shown that live cells actively reduce part of the assimilated iron(III) to iron(II), the latter amounting up to 33 % of total cellular iron after 18 h of growth, and 48 % after additional 3 days of storage of the dense wet cell suspension in nutrient-free saline solution in air at room temperature (measured at 80 K). The cellular iron(II) was found to be represented by two quadrupole doublets of different high-spin forms, while the parameters of the cellular iron(III) were close to those typical for bacterioferritins.